Assuming the flapping power of the wings are magically provided, so that the girls don't need to have shoulders a meter wide (which has to be the case anyway, like Suika's strength coming from those thin arms), do the wings really have to be around the center of mass for balance? I don't know a terrible lot about aerodynamics, but I always thought between shoulders (location of the shoulder socket to be specific) and waist was okay.
Also when they stay still in the air. It would help to have more mass below the wings than above, so that they hover the right way up.
Interesting topic to study about. I guess I'll take time to learn a bit about aerodynamics when my vacation starts.