Need Advices to Setup Rear Suspension

???? One inch of travel(1") Is not enough.
Jack your back bumper up until your tires are off the ground and then see how much travel you have left. On inch is not enough.
Just the force of the suspension under launch, will push the suspension up(push tire down) more than the droop you create by letting the suspension droop/ hang.

In the video what i see by starting and stopping the video as you launch is....
front end comes up(weight transfer) rear start to rise,(tire loads) then you see the rear suspension stop rising, tire unloads and slip. front tire returns to the ground. Rear suspension does not move from that point on. tire goes down the track bouncing like a basket ball sort of :D
Just my thought, could be wrong.