P-valve CLOSED --> Stiffer spring will do it :)

[Dino86]

I'm wondering if I can "pimp" the brake proportional valve by cutting the spring to increase rear brake pressure.
If possible I want to avoid installing adjustable valve for MOT ....

My question is basically:

Will a shorter spring in the p-valve reduce or increase pressure to the rear brakes?

In other words, does the spring close the rear outlet based on a certain hydraulic pressure (differential pressure)? In this case a stiffer spring will increase the rear pressure?
Or
Is the spring deciding the opening of the outlet? This includes Pressure delay between Front and Rear brakes.
In this case softer (cut = less pre-load) spring increases the pressure and reduces delay...

The more I think about it the less sure I am