Droop is a tough one for people to understand. I prefer to use uptravel. Slide a ride height gauge under one end of your car. Lets say it reads 5mm, which would be your ride height. Then, hold down the wheels at that end of the car, and pull the suspension up as much as you can until it bottoms out, then slide the ride height gauge under your car again while holding the suspension in its upmost position. The difference between that measurement and your ride height is your uptravel. Lots of guys use that instead of droop since it's a more universal and consistent way to measure and express that particular setting. It's essentially two different ways of measuring and explaining the same variable in your car's setup.
Almost every foam/carpet setup I've seen uses 2MM of uptravel at each end of the car. It's a VERY powerful adjustment, so it's good to make sure you've got it right.