In tunnels it is easy to actually measure the pressures all over the top and bottom surfaces of a wing at different angles of attack. (This is done by making many small holes in the surface of the wing and connecting these 'pressure tapping points' with tubes inside the wing to a bank of manometers or U tubes containing fluid. Naturally the fluid gets 'blown' up at the places where the pressure is increased and 'sucked' up where the pressure is lowered. The height of each column is of course proportional to the local pressure at the tapping point and providing you know the specific gravity of the fluid in the manometer the actual pressure - positive or negative - can easily be calculated.)
That's an ingenious way of measuring I hadn't thought of!
You will have to take my word for it that at angles below the stall the suctions are relatively much larger than the positive pressures. If you doubt my word (and why not for goodness sake) you could examine any suitable reference work on such activities.
I don't believe I said anything that would contradict that. That's what I was meaning when I said that a piece of plywood would fly, based on the same principles as a normal airfoil, when below its critical angle of attack.