The fluid tail Fiat has a lot going on. It is a box cavity like the prior example but it is oval instead of square cornered. The screen with the half-circular cutout is the perforated base plate. There are also centrifugal fans built into the wheels to pump air into the lower corners of the cavity to compensate for the wake of the tires.
Here is aerohead's explanation of 'tearing edges':
The idea is that in buffeting side winds the point of separation is fixed instead of wandering around. You can see an example by comparing the latest Prius to earlier models.