CG may be able to be moved back... I like mine as far back as possible so that the airplane is still controllable with an empty tank... Take your plane up an run the tank through it/put 1/2 a tank in it and take off... run till she is about to dead stick, or untill she does... If it still glides down good you can add more weight... Trust me all competition aerobatic planes/models have their CG at it's aft most position... On the knife edge issues does your wing have any dihedral?? If so it will be a little more difficult to hold knife edge... Her is a pic of my big stik 40... I had it at the recommended CG and wanted to move it back to be more aerobatic... 3 OZ of lead... Fly's great...