diff --git a/src/05-derivatives/05-diffusion-derivatives.md b/src/05-derivatives/05-diffusion-derivatives.md
index f3e0813f..340cd095 100644
--- a/src/05-derivatives/05-diffusion-derivatives.md
+++ b/src/05-derivatives/05-diffusion-derivatives.md
@@ -109,6 +109,10 @@ rather than the image data).
                     <source_keywords>[_space-<space>]_model-<label>_model.json
         ```
 
+-   Files "`<source_keywords>[_space-<space>]_model-<label>_param-<param*>_model.json`"
+    are REQUIRED to accompany each NIfTI file individually, as they MUST specify the
+    [data representation](#data-representations) used for each image.
+
 -   File "`<source_keywords>[_space-<space>]_model-<label>_model.json`"
     provides basic model information and [input parameters](#paramdef-input).
 
@@ -338,15 +342,15 @@ in order to produce a [directionally-encoded colour](#data-dec),
 
 ### Orientation specification
 
-| **Key name**                | **Relevant [data representations](#data-representations)**                                                                                                       | **Description**                                                                                                                                                                                                                                           |
-| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| `AntipodalSymmetry`         | [Spherical coordinates](#data-spherical), [3-vectors](#data-3vector), [spherical harmonics](#data-sh), [amplitudes](#data-amp), [parameter vectors](#data-param) | OPTIONAL. Boolean. Indicates whether orientation information should be interpreted as being antipodally symmetric. Assumed to be True if omitted.                                                                                                         |
-| `Directions`                | [Amplitudes](#data-amp)                                                                                                                                          | REQUIRED. List. Data are either [spherical coordinates (directions only)](#data-spherical) or [3-vectors](#data-3vector) with unit norm. Defines the dense directional basis set on which samples of a spherical function within each voxel are provided. |
-| `FillValue`                 | [Spherical coordinates](#data-spherical), [3-vectors](#data-3vector)                                                                                             | OPTIONAL. Float; allowed values: { 0.0, NaN }. Value stored in image when number of discrete orientations in a voxel is fewer than the maximal number for that image.                                                                                     |
-| `OrientationRepresentation` | All except [scalar](#data-scalar)                                                                                                                                | REQUIRED. String; allowed values: { `dec`, `unitspherical`, `spherical`, `unit3vector`, `3vector`, `sh`, `amp`, `param` }. The [data representation](#data-representations) used to encode orientation information within the NIfTI image.                |
-| `ReferenceAxes`             | All except [scalar](#data-scalar)                                                                                                                                | REQUIRED. String; allowed values: { `ijk`, `xyz` }. Indicates whether the NIfTI image axes, or scanner-space axes, are used as reference axes for orientation information.                                                                                |
-| `SphericalHarmonicBasis`    | [Spherical harmonics](#data-sh)                                                                                                                                  | REQUIRED. String; allowed values: { `MRtrix3` }. Basis by which to define the interpretation of image values across volumes as spherical harmonics coefficients.                                                                                          |
-| `SphericalHarmonicDegree`   | [Spherical harmonics](#data-sh)                                                                                                                                  | REQUIRED. Integer. Maximal degree of the spherical harmonic basis employed.                                                                                                                                                                               |
+| **Key name**                | **Relevant [data representations](#data-representations)**                                                                                                       | **Description**                                                                                                                                                                                                                                                                                                                    |
+| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `AntipodalSymmetry`         | [Spherical coordinates](#data-spherical), [3-vectors](#data-3vector), [spherical harmonics](#data-sh), [amplitudes](#data-amp), [parameter vectors](#data-param) | OPTIONAL. Boolean. Indicates whether orientation information should be interpreted as being antipodally symmetric. Assumed to be True if omitted.                                                                                                                                                                                  |
+| `Directions`                | [Amplitudes](#data-amp)                                                                                                                                          | REQUIRED. List. Data are either [spherical coordinates (directions only)](#data-spherical) or [3-vectors](#data-3vector) with unit norm. Defines the dense directional basis set on which samples of a spherical function within each voxel are provided.                                                                          |
+| `FillValue`                 | [Spherical coordinates](#data-spherical), [3-vectors](#data-3vector)                                                                                             | OPTIONAL. Float; allowed values: { 0.0, NaN }. Value stored in image when number of discrete orientations in a voxel is fewer than the maximal number for that image.                                                                                                                                                              |
+| `OrientationRepresentation` | All                                                                                                                                                              | REQUIRED (unless [scalar](#data-scalar) [model-derived parameters](#paramdef-derived)). String; allowed values: { `scalar`, `dec`, `unitspherical`, `spherical`, `unit3vector`, `3vector`, `sh`, `amp`, `param` }. The [data representation](#data-representations) used to encode orientation information within the NIfTI image. |
+| `ReferenceAxes`             | All except [scalar](#data-scalar)                                                                                                                                | REQUIRED. String; allowed values: { `ijk`, `xyz` }. Indicates whether the NIfTI image axes, or scanner-space axes, are used as reference axes for orientation information.                                                                                                                                                         |
+| `SphericalHarmonicBasis`    | [Spherical harmonics](#data-sh)                                                                                                                                  | REQUIRED. String; allowed values: { `MRtrix3` }. Basis by which to define the interpretation of image values across volumes as spherical harmonics coefficients.                                                                                                                                                                   |
+| `SphericalHarmonicDegree`   | [Spherical harmonics](#data-sh)                                                                                                                                  | REQUIRED. Integer. Maximal degree of the spherical harmonic basis employed.                                                                                                                                                                                                                                                        |
 
 If `AntipodalSymmetry` is True, then no constraints are imposed with respect
 to the domain on the 2-sphere in which orientations may be specified;