It took a while adjusting it, but the 1st generation Kevlar, aka “Fritz,” I received in 1986 eventually fit as well and easily as my M1 steel pot. The current Kevlar is a 2nd or 3rd generation, with a less pronounced back flare to protect the back of one’s neck, due to nearly all troops wearing body armor (aka modernized ‘flak vests’ of Vietnam). the original Kevlar and modern body armor causes the front of the helmet to cover one’s eyes, aka Beetle Bailey.
Yeah, I wore the original k-pot for several years until I was assigned to the Stryker brigades. They were a royal PITA when worn with the old flak vests. I don’t think I ever wore an IBA with an old k-pot.
The flak jacket—>IBA—>IOTV evolution was a very welcome one as well.