Actually, this is a optical illusion, her calves are pressing on her thighs and buttchecks, making them bigger, pushing them, add the angle of her leaning fwd...this is a pose the photogs are using to make it seem like the girls have ass...I've seen this used multiple times---and then you see the girls stand up...ass is gone
the French chicas is nice, but again, look how they have her pose, much like Arnold and his twisting shots, the one leg out, and twist gives the illusion she has ass...by spreading the legs out.