Hello Dear Smart Friends, I have bought my girlfriend a retrofit system for parking aid for your Smart. There are 4 parking sensors and a small box incl. speaker for the beep. The instructions say that I should drill 4 holes, but I have now looked at the Smart, and there are already 2 holes there. 1. Question: What are these holes? I removed the protective flap and they lead into the empty, can I use these for the parking sensors? The parking sensors are however slightly smaller than the holes in the rear bumper large (of diameter). 2. Do I need 4 holes for the Smart at all or are 2 enough? Nice greetings and I would be happy about help.