Hi. I noticed the same thing on the left rear of my vehicle once I replaced the air bags. Thought I had maybe done something wrong during fitments but after reading some BMW literature on the suspension where they mention a +- height with allowance of 10mm (1cm) I was satisfied. I've measured the height a few times since and will pay that most often after driving it, including passengers getting in and out of the rear, both left and right seem to be identical in rest height so it's probably just a result of the play in the mechanical linkages between strut, sensor, and chassis that sometimes produce the minor differences (which BMW allow for in).
Hope this helps. My tyres are not old enough for me to notice any uneven wear patterns so can't help you there.