[Perfectlap]

ok I think I see what you are trying to do. You are working on a bumper project, so everything below the rear trunk and tail lights?

Sometimes when I look at the Boxster from the side (left or right) It does seem to me that the stock bumper sits up too high. Meaning there is too space bettween the the very bottom edge of the bumper and the ground. I noticed this especially on the TechArt Caymans.

tHE design you have is too busy. I think making extend lower would be a good idea. Perhaps with some kind of opening for the rear exhaust. Keep it simple.
I wouldn't add all these openings. Maybe I might add the 911 'fins' that you might see on some models, they go on the extreme left and extreme right.