ORIGINAL: PAINLESS
I could be wrong, but isn't lift created by air flowing over both upper and lower surfaces? If you eliminate one or the other the remaining surface is rendered ineffective. Like the area of wing blanked out by the fuselage reguardless of whether it is on top or bottom of the fuselage.
I have heard before that a high wing generates less drag at the fuse/wing joint than a low wing, it would be interesting to know just how much.
The Dodger had the area of the fuse just behind the wing pinched together, which was said to mimic wing fillets.
Painless,
It's true that lift comes from the pressure difference between the top and bottom surfaces, but it does intuitively seem to me that it could matter which surface you replaced with a fuselage. I think that the bottom surface of the fuselage would be better at generating the high pressure than the top surface of the fuselage would be at generating the low pressure. The flow, and resulting pressure, on the top surface of a wing can be quite dependent on the shape of the wing. The flow on the bottom is a little less sensitive. This is not a rigorous analysis, but it does make sense to me that it would be better to preserve the top surface of the wing than the bottom.
banktoturn