Shouldn't make any difference.
In the real world in would as it affects the aircrafts centre of gravity and inertia. How it is modelled in Aces High is another thing, perhaps just on the weight. So I would be inclined to leave it on auto.The only time I manually select a tank is when it gets hit and leaks, then I try to burn off what I can before it all leaks away!
I believe the Spit's tank were one above the other directly ahead of the cockpit.