For the 4 wing servos, I thought I could programme in a different CENTRE servo position for each flight phase, but the transmitter does not allow you to do this.
Use offsets (OFS AI and OFS F) rather than servo centre to get your neutral flap point, then use fix F for setting flap prefixes for each flightmode (make sure you have flightmodes turned on)
If I remember correctly, the Mimic is a 4-servo wing. It means that the setup is a little trickier than with a 2-servo wing.. but the sx can do it
Dont confuse this with the FIX switch on the transmitter.... the FIX switch is what you will use for launch prefix... if it is activated, then the values set in Fix R, Fix E and fix A are applied to those surfaces which the momentary "fix" switch is pressed.
The sx manual is very complete... but you have to read it over and over before things become clear. If you go through the "GLider" model type setup instructions step by step it actually tells you everything you need to know. The trickiest bit I find is getting the offsets and throws set up.
Where are you based?