The geometry between shoulder, eye, jowl, neck, and hand is everything.
Also stance. The M16A2's stock was lengthened from 13in to 13.5in at the behest of Camp Perry types who typically use that gay-assed bladed offhand stance. When we started going to war in addition to going to the range we found the new longer stock sucked balls for about 99% or users, regardless of height, arm length, inseam, shoe size, astrological sign, etc,etc..... This is a much more effective stance:
