You just make the head as big as you normally would, I don't see or have ever experienced a reasion to make special video game proportions to realistic human models. I can tell you that heads don't grow much respective to body height. This means that small guys have big heads and big guys have small heads (compared to the body height, in reality their heads are about the same size) This way you can also guess height of people on TV, emphasis on guess because there are allways variations.
The guys feet in OPs picture kinda look way too small and almost comical compared to his burly upper body and arms.
I only know that you want your world/level geometry about 1.5 X times bigger than your player, otherwise your world feels small and crammed. I can't tell you the reason why this is like this, but it is.