I looked at several of your photos of the park sensors - in the rear bumper. Like mine, they are not flush but appear to be perpendicular to the ground. Is this the correct installation or should they be flush with the bumper?

 

I think it depends, because there seem to be two different types of sensors. One flush and one not so flush w the bumper (and also bigger).
There is one type on the M-sports bumpers (I think it's the older type of sensor, also found on pre-LCI cars with std bumper) and different type on the std bumper with a more subtle sensor (atleast on LCI cars).
However, I'm not 100% sure about this, maybe someone can fill in here...