Well well well, welcome to the club!
I have been suffering this for 2+ years, with M Performance Springs and also Eibach springs on my M235i.
I fitted a BMW spring shim (6mm - works out to be 10mm at wheel) on the drivers side (Passenger side for you) and that didn't solve the problem, rather raised the oppose side also! I also fitted a powerflex 11mm spring shim, but that didn't resolve either. More recently I disconnected the NSR antiroll bar droplink and guess what... the NSR dropped!
So in a nut shell I believe this issue to be rear roll bar torsional preload. I will try fitting adjustable droplinks to see if it resolves the issue.
For me apart from the asthetics, it affected the handling and shifted the roll centre away from the middle of the car at the rear. I haven't solved the issue yet, but think I might be almost there.
This thread is also relevant:
https://www.2addicts.com/forums/show....php?t=1576121