Mike,
Are you doing the following
Balancing it upright?
Balancing it will the fuel tank empty?
Balancing it right on the main spar which is 3.5 inches back from the leading edge, I think? (I used to have one but I cannot remember the exact measurements in inches but it is right on the main spar)
you can always move the battery.
I used to have the same plane and setup and I needed no weight and had the battery right behind the full tank (between the servos and the fuel tank). That was a JR600MaH battery at something like 4oz's
Let me know, I'll be glad to help ya out