I have read somewhere that the deck lid vents were redesigned/relocated when the rear sail panels were cut down for the TC variant, so as to maintain their function with respect to the slightly altered aerodynamics.
As for effectiveness, maybe it's time for a yarn test. Curiosity is piqued, now. Once mine is making noise again, I'm going to give this a try. I'll report back, but it won't be until spring at the earliest, so don't hold your breath.