Try pulling your shots when the PI pressure is at the same value and see if that has any effect on the catch point.
My guess is that you will find that your catch point is lower when the PI pressure is higher. I usually try to pull my shots right after the pstat clicks off.
You get a lower catch point with better puck saturation. Besides a higher preinfusion pressure, you could also try tweaking your grind to be a bit coarser or dosing less, depending on how you want to balance your shots.