@ imperial shifter:
Please do not mix up TAPRV (Trim Air Pressure Regulating Valve) and TAV (Trim Air Valve).
With the TAPRV you get air in the hot air system. The valve is not regulated by the zone controller (or ACSC 1). The controller can (simply said*) only turn it on or off.
The phrase "regulating" belongs to the "pressure". It regulate the hot air manifold pressure to 4 psi above the cabin pressure and this pressure regulation is controlled pneumatically by the valve itself.
Only the TAVs are "regulated" by the controller (ZC or ACSC) to get the wanted temperature in each section.
*) in addition, if duct temp goes above 80 °C, the controller can force a 50% pressure reduction via solenoids.