there is so much more to port area than going with a general rule. that's a lot for aero ports. I personally use 4-9 sq in for aeros, 6-10 sq in for round, 12-16 sq in for slotted or rectangular. i use BBP6 so that there is no question when I start building. I've had many installers that I work with try to tell me "you're wrong" when I tell them what I'm building for a specific enclosure but once they see how it plots on a graph compared to what they think they know. when it comes to port area and you are wanting to go "small" you'll most likely encounter port noise. I always stay between 20-30 m/s for pv which the rule of thumb usually keeps pv in the safe realm of 15-25 m/s. when building port enclosures I personally believe it's all about getting the velocity right. if I plot an enclosure and the velocity is less than 20 m/s, I keep making adjustments till I get over the 20 m/s mark. when i first started off I thought I knew what I was doing but I look back and see there was little to no velocity. those boxes sounded good but now I'm more about the velocity. now all my boxes now sound awesome and move air like fans w/o noise.