We suggest mounting it as close as possible to the firewall. The fuel tank location is critical for fuel delivery.
I would suggest trying your tank location on the ground and check the running thoroughly before flight testing. ie: holding the model vertically and watching for sagging from the engine.
ORIGINAL: Rudeboy
As these bigger engines run a crankcase pressure system, will it be possible to mount the tank further backwards over the CG?
If it uses a check valve and crankcase pressure, there should be more then enough pressure to supply the carb with fuel as I see it.