Bladder is apparently sensitive to slope...

I may have made a discovery yesterday, and figured I'd toss it out and see what happens.

I've noticed through the years that most gas tanks are somewhat sensitive to the vehicle's level. I usually play around with different pumps to see which one gives the "best" filling results - close to full before the nozzle shuts off, no vomiting, etc. I filled our Prius on Friday at one pump, with the right-front of the car slightly downhill from the rest of the car. It took a bit over ten gallons, which was about what I expected based on mileage and the single pip on the gauge. The first pip disappeared at just over 150 miles on the tank. I filled it again Sunday morning in preparation for another long day of driving, same station but on the other side of the pumps, so the gas cap was slightly downhill. It took about 2/3 of the fuel it should have based on miles driven versus displayed MPG, and the first pip went away at under 100 miles.

IMO, this pretty well verifies that the best way to get a complete fill is to have the gas cap pretty much the highest point on the car - this apparently allows the bladder to expand completely in the tank, without binding. What say you?