I remember friends of mine that worked for NHRA division seven saying 3.0 inches off the ground to, I think, the center of the bulb and receiver unit on the staging beams, 6.0 inches on the other end bulbs and recievers
As far as heads up stripe takers NHRA limits the 36.0 inch rule max from the center of the spindle to the front due to the funny cars guys moving the front air dams out further than those cars body styles came with back a long time ago