Hi, Firstly i'd let the air out of the shock to check it's not stuck down, air seal fault causing the air spring to work backwards. If it is the shock will compress fully with any weight on the rear end.
if not:
Set the sag to 1/3 of total travel, this is the distance from the end of the air seal in the air can to the end of the plain shaft/body tube.
Do this sitting down, don't bounce with the Propedal off.
Try the rebound at 3 clicks off full slow, shouldn't sit down in travel and shouldn't bounce you out the saddle when riding over bumps.
Hope this helps, remember that on really big hits/bumps you should be getting full or near to full travel. However if your regularly bottoming out on a ride the shocks too soft, try increasing in 10psi increments.
See how it goes tomorrow, post again if still not sorted with issues and I'll see if we can work it out.