I have my R-10's, used to be K701's, HE-5's, 02's, SR-Lambda Pros, ESW-10's, etc. all maxxed out. I don't have that large of a head. I'm going with the "top of the head to ear position ratio" theory.
I was on of the only people who needed a medium in the Qualia 010's.
It is one of my crosses to bear. When it comes to motorcycle and mtn. bike helmets, I only use a "large". Not an extra large, or XXL. I only weigh 180 lbs.