It's an ergonomic flaw. BMW fixed it on an LCI where controls are like 1-2cm closer. I'm considering to buy the LCI control panel actually from junk yard if i can find one.
When I don't think about it, i hit rear window switches, when I do - i don't miss. It's one of few minor ergonomic issues with E90 (other being steering rim covers top of dials and the lock door button in center console is a wierd place).
'07 TiAg E86 Z4 Coupe 3.0si