Hi - I did have similar issues a few years back... as far as I remember I raised & lowered the car via a diagnostic machine (my pal local garage)... I measured correct height (bottom wheel rim to wheel arch to get correct height) ... the readings from sensors come in at all different values - this does not matter - you then tell the diagnostic it is level & module remember those figures. If one corner sags more than 9 to 11mm after that, SLS inactive will come up on dash......
However I could not get the system to re-activate even after clearing codes.
I went to local independent BMW guy who had more sophisticated S/W.
He had SW prog that takes you step by step through the process.
It is weird - you cant stop mid program or it messes up.... he showed me it step by step till it completes - again involves raising & lowering to correct (tape measure) height... then locking off etc etc... we had 2 big guys sitting in the boot/trunk so that when it pumped up we were sure it was correct & stable. Then locked off (saved) various voltage values as 'level' The guy charged me £40 as it was quite a quick process... 20mins ish. Hope this helps. Malc