Nick, if the pressure distribution changes when the lower aerofoil is reduced in angle then you have proved the pressure theory of GE.
The increased pressure below the wing produces an increase in CL and therefore lift which allows you to reduce the pitch angle to stop it climbing (exactly what you do in an IGE hover). Not only is the Cd reduced by the increased pressure making the wing think it is bigger than it is and therefore more efficient but the further reduction in Cd caused by reducing the AoA means less power needed to drive the wing through the air (just like in an IGE hover).
It is a little like chicken and egg, once you have compensated for the extra lift in GE by reducing the pitch angle, THEN the pressure distribution will be the same and you will have produced the same lift (ie just enough to keep the wing level) but with less AoA and consequently less drag.