What I mean by "small heads" should be pretty self-explanatory, but it would appear that their heads are too thin, especially when you consider that they're wearing bulky metal helmets. Moreso on Aile than on Ashe.

And by "thickness", I mean how they're wide and somewhat figure-less, yet wearing skin-tight suits with no bulges or signs of fat whatsoever. Thus, they're just oddly thick, yet not fat.