Never heard that tidbit before and can't recall reading it in the zeroing chapter from Shoot to Live. If that were true, wouldn't it also hold true for the peep, thereby making a mockery of the sight graduations?
I've got some ammo left over, I'll try it out with a spike mounted and let you know.
You know, if they issued Rangers bayonets, we'd just use them for roasting marshmallows.