I wouldn't worry about the 20% extra camber, it's actually more than likely improving your handling. The negative camber purpose is to load the suspension to deal with the massive side loading during cornering. You can rest assured the negative camber is zero during hard turns. The fronts work the same way. Look at a Mercedes when the wheel is turned full, the wheels must be leaning 5° or more. BMW do the same. The fronts negative camber only kicks in when steering but since the back don't steer they are preset to negative.

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)