For fixed wing where you want the servo in the middle when the stick is in the middle you generally want the output min, neutral, max to be 1000, 1500, 2000, but there are many ways to set this up. If your airplane was already flying and you are going to use PPM or PWM to talk to the FC, then you may want to copy the output settings from the input. Lastly, you may want to tweak the neutrals a little if you want it half way between two of the servo splines.
What happens is that the input min neutral max get translated into a number -1.0, 0.0, +1.0 (and everything in between) and the outputs translated the -1.0, 0.0, +1.0 into whatever min, neutral, max it has
For Sbus for instance the inputs may typically be 172, 991, 1811 and that needs to get translated into 1000, 1500, 2000 for the servos to work right.