Thanks Martin, for the info ... now I figured out an additional method that works for manual modes.
A third source into the mixers:
S: 3 6 9000 9000 0 -10000 10000
S: 1 4 0 -20000 10000 -10000 10000
S: 0 2 8000 8000 0 -10000 10000
Then RcAux can be used as a kind of tilt trim. And with a mixer in the tx it can be assigned to the pitch stick that brings the desired mode back. And to control the amount of hanging tail in assisted modes as well.
But how can I get rid of the 2150us limit?
"pwm max -c 56 -p 2450" and "pwm min -c 56 -p 650" result in the desired min pwm but max pwm is limited at about 2153us
2450us would be the perfect value to follow the full path of the Convergence´s mechanical servo system (and a way to use PX4 for my Taileron Vtol project)