That depends on your engine/pump.

I have a 60 size GP Extra300 with a YS 91AC engine on it. The YS has a built in pump and the tank is right on top of the wing at the CG (a distance of about 12 inches)

I also have a 33% GP Extra 330L powered by a Zenoah G-62 gas engine with the tank also on the CG which in this case is about 2ft. So, it really depends on how far up your engine can draw fuel from.