I moved my seat back by cutting some off the bottom half of the "C" springs,
moving them back and drilling new holes in the fenderdeck.
I then added 2 coil springs for support (JD M89540 about $8 each).
This gave me about 2" more belly room and the seat still clears the gas tank fill neck.
Downside, the seat position is no longer adjustable fore and aft.