I have been thinking about port air flow for a few years. Constraints are mostly not having the equipment to test theory in actual applications.
I noticed at a young age how water would not fill a round culvert and the creek would over flow a road with the culverts 2/3 full. So the engineer would need oversized culverts to get the flow needed due to those unbreakable laws of physics.
Some 30 years later after reading Bose patents on the oval shape of their ports, I knew some speaker designers were aware of the weakness of round ports too.
In time I bought a high end muffler and exhaust pipe for a Honda trx400. I was trying to squeeze a bit more power out of the dated engine design. It ended up way too loud. Couldn’t ride with out hearing loss danger. But I liked the increased power from the improved air flow. I found they made a “quiet pack” for the muffler and ordered one up.
It turned out to be 3 different size steel tubes welded to a flange to seal the empty space between the tubes. Then the side of the tubes inside of the muffler is cut at an angle. The results are impressive. Very little loss of air flow (power) but the system is now suppressing almost all of the harsh noise.
I’m guessing they are on to something here. I think an oval port is the easy answer, but different size PVC pipes with gaps sealed with silicone and glued into a flange is on my list to try for sure. An angle cut on the “inside” will no doubt make the port do its job over a wider frequency range.
Good luck finding box tuning software to model that though. It will be trial and error for sure.