Listening to this video tells me that the six-port row must be on the top of the chopper, because inside the rotor, when you have the bottom row open, the blower's air going through that row is going to be compressed by the air circulating in the top row, which is closed momentarily, so you'll have pressure building, because there's only a certain amount of air that the blower can expel under a certain rotor-speed. Think about a rotor with really small ports compared to a rotor with larger ports - the rotor with the smaller ports is going to put more pressure on the blower, though what I just said is only partially an analogy, 'cause that and a Thunderbolt's HI-LO operation are worlds different!
Then, when you have the top row of ports open, there is no air above it to cause pressure buildup, and you also have somewhat greater suction of the chopper.
Wait, I've just seen a picture, and the row with more ports IS on the top. I'm right. LOL!
