Tough to say, really.
I’ll speculate that everone is a bit different as far as shape goes. Pretty hard to measure, too. I guess you just find tubes of different size and try to see which one you can cram your cockhead into. Once you cannot do this and have to move to a larger size, you will have gained. Can’t really see using a tape measure to do this very easily and I have tried…the coronal ridge always presents a problem there. If I recall correctly, it was a fella named Alcatraz who claimed his head was “nearly nine inches around at the meatus”, which causes some anatomical confusion for me, provided I recall correctly. At any rate, regardless of where that girth is, that’s damn nearly the size of a beer can. Folks requested a photo in disbelief, but never got one. One can assume some guys just have a more readily expandable head than others. I too, noticed the head getting engorged during hanging sessions. Especially in the early experiments and over-wrapping sessions. Oddly enough, that amounts to a 15 pound “uli” for twenty minutes and although it wasn’t intended to increase head size, the head did not appear to get much bigger normally, if at all. Hence, I don’t do “ulis” anymore…can’t really see them working to any great effect on me. I have since used less wrap and less blood in the head and found greater confort at higher weights for longer, multi-session hangs. Sorry to ramble. groa