How does it control exactly what psi boost is used????

I have a set of air injectors........


And I had a fooking good look at the boost duty mapping feature!!


BUT..... This is in percentages of injector open/closed at throttle position versus RPM.

Now this has got me confused (doesn't take much!!) How do you specify/control the boost level!!

As I know the air injectors can run 'indefinite' boost by staying shut!!

Is it anything to do with the size of the jet??