I'm not sure if it's how I'm adjusting appearance settings, or if males just generally have a smaller appearance. Mostly comparing Nords here. For example, Lydia's head "fills out" a Steel helmet well. My character is built a bit like Farkas, and the helmet looks gigantic on him. It almost like females in the game had a completely different artist. They just look better, cleaner, have well proportioned heads, etc..

I don't know about heads specifically, but I've always thought female Nords look bigger than the males for some reason.