Mine with a Saito .91 balances at the 6" mark. I originally mounted the rudder servo at the back of the wing opening and used pull pulls. It required quite a bit of down while inverted to keep level. Added 2oz to the tail and it flew hands off inverted. So, I moved the servo back to the tail. This thing has a really wide CG range. 6" CG should be easy to do with the OS 70.