When I measure droop above ride height, I check the ride height like normal, then lift the end of the car from the notch in the center of the shock tower until the tires are just touching the setup board. Then measure the ride height again from the same place. Take that height and subtract your ride height and you get your true droop measurement. Weather your ride height starts at 4mm or 6mm, when you lift it, the tires are going to just leave the board at the same time and you're going to get the same "up travel" measurement. The shocks are unloaded at this point so the spring tension has no effect. Only the droop screws and potentially shock length (if they're not long enough) will effect the droop. If the second measurement is 9mm when lifted, if you started with 4mm ride height, you now have 5mm of droop. If you started with 5mm of ride height you'd now only have 4mm of droop. So if you lower your ride height and want the same droop, you need to actually take some droop out of the car for it to be the same. Like I said, those droop gauges usually confuse people more than they help. I use them to make sure both sides are even and that's really it. Hope this explains what I mean. There's really no reason for putting the car up on blocks and subtracting that height etc... All that does is confuse things.