Is it necessary to set shift_width when bam.array ?

[shangguandong1996]

Hi
I noticed in line 430. when get the count of bam, you shift_width to center the read on the cut site

bam_array = bam.array(tss_ext, bins=bins, shift_width = -read_len/2, processes=processes, stranded=True)

But when I check the paramter in metaseq document, it said

shift_width : int
Each item from the genomic signal (e.g., reads from a BAM file) will be shifted shift_width bp in the 3’ direction. This can be useful for reconstructing a ChIP-seq profile, using the shift width determined from the peak-caller (e.g., modeled d in MACS). Not available for bigWig.

In my opinion, the shift_width is based on the single_end and short read length. But now, almost all sequencing is PE 150. So is it necessary to set the paramter?

By the way, I found whether set the paramter will make a great influence on the result. If I set the paramter, the TSS enrichment will be 6 while drop the paramter, my enrichment will be 4.
And the 4 is same as my own R script calculated TSS enrichment.