I ran a VRX kit (and won every championship I entered with it
). Always ran the hardest springs on the front and varied the rear with track condition. I generally tried to run the hardest springs on the rear as it keeps the car flatter during cornering, but if the track is bumpy a softer spring will ride these better and be quicker overall.
That was with pink med rear and jap med front, which is similar to what you've got. Full additive on the rear and none on the front.
The grub screws on the rear shouldn't be used to adjust ride height, use the nuts on the springs for that. The grub screws are used to adjust droop. Generally our carpet was quite bumpy so I used maximum droop (even on new tyres) and just used the grub screws to make sure it was even left to right.