initial240sx

I have the stance gr+ on my S13, last week i tried to adjust the damper so it doesnt rebound a lot, to -7 rear/-5 front, this coilover comes with 15 ways of dampening, -7>0>+8 (full stiff), right?.... well the car behave better, but still rebounds... so tomorrow i'm going to adjust the front spring, i believe if is preload that's way it rebounds a lot... i read in stance page that the oem spring height is 175mm front and 200mm rear.

So with the car lift, how much i need to adjust the spring? i should adjust the collar so the spring height goes to 175mm...? recommendations?

also i dont know is my knowledge of preload is right...