I liked the drumroll.
Thanks, I'm cheese all the way OK!
Okay, seriously, for what car are we thinking here? The Beetle/Super Beetle has at least four rear window configurations. Then, there are Karmann Ghias, Type 3 Fastbacks, ...
Initially and specifically, I'm thinking about the type 1, but the concept could be used on many.
I'm also wondering from the standpoint of function. Using the New Beetle as an example, there are two main spoilers used. One is the electric one above (or if you prefer "in front of") the rear glass; the other is a static, crescent-looking contraption below the rear window. I have to wonder how effective the latter is despite its larger size.
Precisely, the wings lower down I suspect aren't nearly as efficient in creating downforce as the wings higher up. I was in fact referring to the electric one. VW put it there for a specific reason, perhaps one being looks, but they could have put it at the bottom of the window, instead they chose the top.
I bring this up because the rear window on any of the Beetles is lower than the roofline to begin with. I'd be more concerned the accessory did nothing at all than it pushing in the window.