Neil you can feel confident on moving the cg back with confidence. I have mine at about 170mm and it shows no sign of being a tail heavy bird.

You need to try a wing tip spin using opposite aileron and rudder and full down. Reflex mix also helps. Does the most beautiful wing tip spin I havel ever seen.

I have retired my Magic Extra today because after about 30 flight on my seduction I was shocked at how terrible the Magic Extra was in comparison. Gonna go the profile route as a true throw around.