off my head
the wastegate duty solenoid in the near side wing, is what "controls" the wastegate! is as much that its that what opens and closes very fast and pulses air down the line to the actuator, but does that sense boost? i dont know?
i think the ECU senses the boost, (via what im not sure??) then sends current to the WDS to increase or retard the actuator pulses ( increasing or decreasing boost)
line 11 maybe, that goes from the manifold and sends boost and vacuum pressures to the MAP sensor in the Solenoid box?? maybe it gets its signal from there??? its the only line i can think that takes manifold pressures to the solenoid box!
i think your problem may lie with the WDS, the actual actuator, solenoid box internals, and as i said maybe but not too likley, the restrictor pill in line 23
have you tried taking off the turbo/actuator tpiece line (line 23) and running a solid line from turbo nipple to actuator to see if you get the .5 bar boost pressure preset (for lack of a better phrase lol)
this was you take away ANY ECU and WDS control and you can cross off the actuator, as if you still get big boost with this, you will have a possible sticky actuator perhaps