I don't know for sure that a person can ever show proof positive of shrinking a group a few tenths.... mathematically you should.. BUT gain a bit of extra wind resistance and that, at least to me, can save you... Having won matches a number of times by one point, and having had one point there that was barely hanging...
I recall one time it was vivid for me.... I actually won the state match 800 yard line of a palma match with my service rifle.... the top couple of shooters all shot 149s, me included. We ALL got burned by that one unseen change.... and I won only by xs.... BUT it was wildly obvious that teh folks shooting bolt gun 308s were out further than what my 90 was... in fact if it had been just about an inch less in wind drift..... because they were outer 9s, I was an inner.. that was mostly folks that I knew shooting 190 and 210s in the 308s...
