I have the GP Sukhoi SU-31 and I put a RCGF 50 CC engine in it. Perfect fit. However, they are calling for the CG to be 5-11/16" from the leading edge and I am nose heavy. That measurement is about 2 inches from the back of the spar. If I get on the edge of the spar, it balances. It says that you can move the CG up 3/4" after the maiden flight if necessary, but it still won't balance even with weight added. I have everything moved back as far as I can in the fuse and have added several ounces with no balance. How critical is it. Will it work if you just get it close? Any suggestions?