All tuned RSTs should have had the pressure actuator adjusted. It's used for the on boost enrichment. It adds a percentage of extra fuel to stop you melting your engine. When you have your boost incresed, the tuner should also adjust the pressure actuator to increase the percentage of fuel added.

There is only so far you can adjust the actuator. After this, there is more tricks that you can do the the KE jet to get it to fuel more.

This system is quite crude in the way it adds more fuel. The extra percentage of fuel added may well be too much fuel lower down in the rev range, and the car loses a bit of power compared to what it would do at that particular rpm with a well maped EFI system.

My own car has had the pressure actuator adjusted and it needed to be adjusted a hell of a lot to bring the fueling up. Even now, it doesn't fuel enough to cope with 14 psi on a standard T3 about 5000 rpm. I have to change gear at 5k otherwise I risk meltdown.