I have an Aerodeck, but I have the same suspension setup as you have (Bilstein B6 + OEM springs), and yes, the rear gets little suspension travel because the spring is too stretched, getting too stiff at the back. The "solution" I found was to put the 4 shock absorbers on the last groove, which would make the car lower by about 1cm. This will help the spring to have a bit more travel. In a few days I will change to eibach springs.