This also bothered me in Halo 5: Helmets just have random sizes. Most of them are believable, but some are just way too big and others are way too small to fit a human head in.
PLEASE just have a base model of a believable sized head and make the helmet AROUND that model. That way you don’t end up with whatever skull crushing helmet Cambion is supposed to be. Ugh, what a waste of a pretty cool helmet.
I even posted this back in August 2017: https://forums.halowaypoint.com/t/keep-helmet-sizes-the-same/194475 And here we are 5 years later. 