Do you really need such enormous servo horns for a 26% plane for as you said "just sport, regular stuff" type of flying?
I would have thought much smaller arms would have been better. Make sure you use the servo's full travel (ATV set at 100-125%) for maximum servo power and precision.
For precision flying you don't need more than maybe 15-20° of surface deflection, so your servo arm needs to be less than half as long as the arm on the control surface.

Regards,
Magne