Another way is to add a Mixer.
add a modifier
set the input to Flaps servo
set signal curve to 0 at 0 and 100 at 100 which will not affect the trim with the flaps up
give the modifier a name (optional)
add a mixer
set input 1 to receiver channel2
set input 2 to the modifier we just made/renamed
set strength 2 % to 10 (may need adjusting later)
confirm Logic is set to add
Give the mixer a name (optional)
set the elevator servo input to the mixer