OK, I looked up what the official images suggested. Note that pic01 is the rear wheel, pic 02 is of a 996 gen, and pic 03 is of the 996GT2, the first car to have PCCB (?)
In none of the three images and accompanying comments, any note was made regarding the rims. The last image has as comment: " In order to cool the brake disc and brake caliper, a proportion of the air flowing into the vehicle is redirected via air deflectors directly to the front brake system." Again, no note of the rim involved.
Another point: any "thunneling effect" of the rim would have to come from rotary movement of the wheel. Note that at this moment, and also in the past the turbo rims have been ASYMMETRIC! That means that there is only one wheel, for both left and right side. Conclusion; If any thunneling effect exists, the air would be sucked into the wheel on one of the sides. On the other side, air would be blown out. Another effect could be that the inside of the rim wall is tapered. (Getting wider going from the center of the car towards the outside. Then, air "getting thrown to the inside of the wheel" by the rotary movement would also be forced toward the outside of the car. I find this highly unlikely.
I hope this helps in your decision. And now for the pics!
