There is great literature here to read and involve to practical fluid physics, but the real deal is that the uniflow set up does not work, at least for me. I have tried in different circumstances but mostly because I wanted to stop flooding the carb in a high tank set up. According with the magazine review, the Uniflow will prevent the flood in a high tank configuration, in my tests the flooding with a Uniflow system is worst than using the normal tank configuration, maybe because I was using an enclosed system with a check valve at the muffler line.
In a lower tank the fuel does not get to the carburetor easily, maybe, as has been discussed earlier because of the pressure of the fluids that could cancel the effectiveness of the muffler pressure.
The system works better with the tank level with the carb. Providing a constant flow on the fuel, and preventing the engine from a leaner condition with an almost empty tank.
Our engines work fine with the normal configuration an can handle the leaner condition with almost empty tanks (They can not handle an empty tank with either system)
It will be good for all of us to hear from more people that have been using the uniflow set up and to hear from their experiences in a level, higher or lower tanks setups. Allanflowers mentioned something very accurate when he expressed that plane manufacturers does not mention the uniflow system and the reason is simplicity and effectiveness. I just wanted to express my personal experience and I am looking forward to hear from some more experiences.