Your quote from Peter's post sounds correct to me Heinz. The shim could go above or below rebound spring it would make no difference. As long as it was below stub axle it would raise same and therefore lower ride height once compensating adjustment was made to main spring to maintain zero gap with rebound.
I would imagine given the choice the shim or spacer should be above the rebound spring (as in SSL instructions) and so marginally reduce striction between spring and stub axle during turns as the inner wheel becomes unloaded, unless you have lower steering bearings of course, as I have.
