First thing we did was make sure the servo was center in relation to the elevator joiner arm. This meant that the servo arm was not 90 degrees to the servo. It was angled toward the back of the model by about 1 or two servo splines. Now we had a servo arm that was level to the elevator arm if you look at them from the side. No wno need for sub trim and no need for any ATV one way . All 100%-100%
Now I used the outer hole on the stab end and one of the middle holes on the servo end. Not as first set up with the push rod on the outer hole of the servo arm and middle hole of the stab arm and 130% atv one way and 70% the other. After that things were much improved.
I have just come in from the work shop where I have set up a 8511 on the stab of a hawk. I tried the finger test (Put one finger on each stab trailing edge outboard tip and get somebody to move the elevator stick) Set up right the pressure at the back was almost lifting the front end off the bench.
Hope this helps. If not let me know.
Regards Al