IMO, the shock has to be longer than the full drop length. Take a look at a hard leaving car with SS springs and the way the rear section looks when launching.
I go full drop + 2-3"
Check out the springs on this car at 57-60 seconds in. Car goes 1.46-47ish 60'
https://www.youtube.com/watch?t=60&v=rewKjJpqGRs
