Not much to contribute here, but some ramblings...
You talk about pressures at all 3 height settings - Have you measured that with pressure gauges?
The TechStream or obdLink cannot tell you actual pressure in the spheres, as the system doesn't have any pressure sensors other than the one at the pump. The system is made so that if you move from Lo to N, it will compute the pressure at the exact moment when the front level valve closes, and then the rear level valve, and then the accumulator.
So, to measure the pressure, you have to have the heights right (physical, not obd readings), at both Lo and N; and also the obd height readings right; and then, with an empty car, move from Lo to N. That's it, the only pressure reading that means anything without attaching actual gauges to the bleeder holes.
Also the graduation test for the state of the spheres requires that heights, weight and pressures are within specs, and no air bags. It is also possible to have one punctured sphere and 3 good ones, and still get a 75% good reading.
And on dtc's: the ahc system is not good at reporting helpful codes. You really just have to physically check all the basics of sensors, linkages, connectors, valves, and so on.