The uniflow tank was invented by Edme Marriott of Dijon, France. in the 1600's. The tank is closed and air comes in through the uniflow tube that is submerged in the fuel, as shown in the diagram. The best I can do on a scientific explanation is to say that the engine thinks it is sucking fuel from the end of the uniflow tube. So it is the position of the end of the uniflow tube that is critical, not the position of the fuel pickup.

Incidentally Marriott was also the first person to test a model in a wind tunnel.

Jim