he has already said what causes it..
it's the extra long hose to the actuator.
if it was a short hose from the actuator to say the comp cover like the stock R32 turbo or even to the intercooler pipe near the turbo, boost will be around 11-12psi as per stock setup.
now go get a remap of the stock ECU.
I think CEFFIE on these forums should do this for a living.
he know's the RB20 well and can get some decent numbers form them.
free plug for CEFFIE