Uhh: Ianb, thanks, let's see if I can repeat your thoughts, that an upwards 'hump' is also going to cause air deflection away, which is up. SO, that looks like the case like you said, that BOTH surfaces actually send an air deflection, away from wing volume, so upside down has similar action.
BUT, and here is the struggle, I still am perceiving a mention of the principal, if you throw an 'anvil', wearing dollar skates, you move, opposite direction, (due to conservation of momentum).
Do that just means, the upper hump shape will get some DOWNWARD FORCE, a little bit. Why can't I say ' You would crash...downward force could exceed the upward force (supposedly caused by reaction to sending some air downward).
Difficult for understanding.