Source Time Function - output amplitudes

[AashaPancha]

Hello, I have been testing the C6SmoothBump, Ricker, and Gaussian STF, keeping all other source parameters constant:
**source type=C6SmoothBump depth=3000 lat=-41.21 lon=175.01 strike=336 dip=63 rake=31 m0=9.55e14 **
The resultant output displacement values differ by approximately a factor of ten. I would have thought that the source time function would be normalised by the moment so that for a given earthquake magnitude, the resultant ground motion at a specified station location would be somewhat similar for each source type.

I am hoping to compare results to observed earthquake motions, but based on this testing, would like advice on the most appropriate source time function to use.