dunno if you've done this yet but[
eliminate the brackets for the bags if you want the rear to go lower.
i ground off the nub for the spring on the rear control arm and used a uv air air house 1 bag with a relocated air fitting. no brackets used at all on mine
pics of my car here
http://www.canibeat.com/2012/10/zfou...3-bmw-z4-3-0i/