Rene,
Spax is a good move on the back end. I'm running between 4 and 6 clicks up from low. At 4 clicks solo I can actually the damper working and with my wife on board 6 is the sweet spot. Now I also have the magic bump stops fitted and these are progressive in function and this really works well for me.
Cain's upper mount fixings... Well I have them fitted as they do square up the shock mounting better, more noticeable when the suspension is compressed of course.
Avo shocks have suffered greatly from bush distortion and bushes breaking up. so perhaps that might help? I have noticed though that some earlier cars, and I think it possible that this may coincide with the change to the upgraded lower shock mount at the rear hub. had a significantly increased angle to the shock absorber and the mounting pins being in different planes would exacerbate this arc type movement. Perhaps someone knows the truth behind this and will post the facts!