Avios Grand Tundra CG

Can anyone help with a CG issue on the Grand Tundra ? 

The online instructions say 75mm to 80mm from the leading edge of the wing and two online reviews say 60mm. 

I’ve tried 75mm but even with the battery as far back as it will go the nose is far too far down so I’d have to start adding weight to the tail which doesn’t seem right.