The high wingers balance right side up, because they hang better on the
balancer. The low wingers hang better upside-down, so they balance
inverted. You can balance almost any plane on the spar. Aero-batic
planes balance further back than normal so they can snap and spin
better....but they can get nasty.

Swept back wings are another story, as well as double taper wings.

FBD.