I am afraid that what you are describing is an old fallacy. By changing the position of the tank you can control the initial head pressure, but as the fuel burns off the head pressure will still change the same amount. The fuel tanks are about 5" tall, so from the beginning of the flight to the end the pressure will change by about 5 inches of water (convert to alcohol). That will cause the engine to start to run leaner as the head pressure decreases.

Steven