It was Video. He was the guy who bottomed out his TC2000 15's and dented the cones out ward. He modified his ports to this kind of design.
I agree that it does obviously decrease the actual port area by virtue of the center flow guide. I also agree that it seems like the decrease in port area would take an 8" and make it closer to 6" in useable area, plus slightly lengthen due to the flow guides and consequently drop the tune. However why go to all of this trouble if you could just go with a normal 6" port to begin with? I don't think Polk would use it, bother to patent it, create the calculation sheet, get the huge technical write up in Audio and offer it to DIYer's if it did not do something of obvious benefit.
Polk claims that a power port of the same size as a normal port, like 6" vs 6", the power port would be shorter, have much greater useable airflow(output before chuffing)even with diminished useable port area, and provide closer to predicted max output. For instance the port that I attached is claimed to be equivalent to a 14.87" diameter port! I can only assume that this is accomplished by slowing the airspeed exiting the port, allowing much greater airspeed to be useable before port compression /noises/etc., greater effective coupling of the port mouth to the room(maybe some kind of Quasi horn like effect?
). I honestly don't know and I'm not vouching for the reality of these claims, but I may be willing to find out. Maybe this would be something worth checking out for yourself with an old 10 or 12 that you've got lieing around Illka and starting a thread in your test area?