How did you change the stabilizer incidence?
which direction?
-I designed a mount which I shimmed on my patternplanes -others used a screw adj

when you were done with this adj-did you retrim the elevator - very much?
I designed all my pattern types with the thrust line running slightly to a bunch- above th e effective CLof th wings-
the engine/wing and stabs were all 0-0-0 to start
the error allowed in fitting wings to fuselage was 0,to a measured 1/8" positive at the root - the stabs could then be tweaked to get the stab/elevator alignment at "hands off" , about 0-0
depending on the speed desired (pattern) these arrangements varied a little to give the best controllability AND neutral feel.
There is NO perfect setup.