So the axle is not moving in relation to the car, but the car is bouncing. How will tightening the shock do anything? The shock controls axle movement which we don’t have. With the rear ride height, there isn’t much weight transfer. If we go full loose on extension for the shocks does it try to throw the axle out of the car? If not, then is the spring really controlling the axle not the shocks? My idea would be get a good tire pressure setting by having someone take a picture of the tire marks of the launch. Then you know basically what the tire wants. Then I would try to get the axle to move by loosening the extension of the shock all the way and loosen the compression a good bit. It will probably crush/bounce the tire at the hit, but you can start tightening the extension until it slows down. When it is still bouncing the tire just a bit at the hit. Start tightening compression to see if you can hold the axle down through the initial bounce. Just spit balling