The distance between the center of the fuel tank at its design location and the design CG of the airplane is not so much to make that much difference in the moment arm with regard to balance. I'd recommend placing the fuel tank in the design location and balancing the model with the fuel tank empty. Works fine that way on mine.

The Rutan "Quickie" is a different ball game altogether....that one does have the fuel tank centered over the CG and it DOES matter!

Rube