High Wing Drifter,
At the very high angles of attack the delta and swept wings seem to be able to achieve, there must be some kind of blanking effect that must reduce the pressure of the air on top of the wing to some degree.
You are missing another flow pattern which is relevant (especially to deltas) .. leading edge vortex which provides a substantial part of the lift and accounts for the high alpha. Plenty of references around -
for instance. A very common real world flow visualisation in high humidity conditions as in the Concord shot in the previous link. The phenomenon is important in the flight mechanics of many living entities (
for instance).