You will find, that when they're on a running car with exhaust gas flowing, they will open at a lower pressure. Why? The exhaust gas is also exerting force onto the diaphragm through the actual gate...
The R33 connected direct to the actuator should not run over 5PSi.
When the solenoid activates it bleeds off some air, meaning the pressure the actuator is seeing, is lower then what is really there.
IE, if it's really at 7PSi, the actuator is only seeing 5PSi still... If you give it full pressure, it'll open further, and reduce pressure until it sits back at 5PSi...