I suggest cleaning up the aerodynamics of the engine pylon. Add some leading & trailing edge balsa stock to the pylon to smooth it out, & cover it with Monokote (or whatever). The wider, cleaner pylon makes knife-edge flight a breeze with a 46. My current Seamaster ARF has a TT .46 Pro with a 12-4 APC prop & it has unlimited (just) vertical & horizon-horizon knife edge capability.

I have never had a structural failure with a Seamaster & I don't re-inforce the tail assembly or the center-section.