930 seems to have variable height suspension

[reachme]

When she is raised on a lift (88 930 cab all stock-original Bilsteins) I know just how much to shim for all around contact before safely lifting.
After she is lowered to the ground, if I want to re-raise she now sits about 3cm higher. I need to spend 10 minutes reshimming everything and that variance makes me curious. When I put weight on the corner she bounces back up and stops so struts seem ok-is that a reliable test?

So I'm asking the experts, do you think this is due to normal spring action, old shocks, hyper extension due to wheels pulling down that comes back to normal? First contact when coming down is always outside edge of tires that push out as more weight is applied, maybe it's friction of that wheel rubber on garage floor making it sit artificially high until she is driven? 3cm is a lot but I can't be the only one who has seen this. Only threads I've seen so far are "is long term storage on a lift bad" and that's not the question as its not the weight, but where is the elasticity coming from? Where is the most "memory" in the suspension system?

Thanks
Matt

[JFairman]

When you lift a car with trailing arm independent rear suspension the wheels go to extreme positive camber while off the ground and in the air.

When you put it back on the ground the tire tread isn't going to slide out sideways on concrete or pavement so they stay stuck at positive camber and thats holding the suspension from settleing out. Roll the car back and forth or drive it to get the tire/wheel camber and suspension settled and back to where it should be.

What are you shimming? There is no shimming for ride hight adjustment on stock 911 suspension.

[reachme]

Thanks JFairman
By "shimming" I mean the lift arm points need to be flush to the chassis lift points and there are a series of different tools from lift pad extensions, hockey pucks, wood blocks to bridge that variable gap. Not shimming anything on the car.
Thanks for your answer, I'll try that out.

Matt