You can turn that 7 times you won't see more than a 15psi change, The nozzle size is the main factor in the pump pressure. So if you are running a M3 you will not be able to reduce it less than 200psi. The
pressure switch really does little to effect the pump pressure. The only real way to reduce pressure is to PWM control the pump like our controller or reduce the voltage going to the pump. Most vehicles put out about 13.8v while running you can reduce that down to 12v and that will knock off much more pressure than turning the screw.
Or just get a smaller nozzle