Dual-servo elevator linkage geometry
Your going to have problems if you slave one servo into a diferent port on the reciever and mix then together.
You will only be able to trim the one hooked up to the elevator port on the reciever. The other servo will not move with manual trim inputs.
As others have said, you will get a difference in control travel if you use the horn on opposite sides of the servos. Even if you mount the servos on top of each other and the horns appear to be swinging in the same arc, they will move differently.
I know this because I tried it on a Sig Cap 231 Breitling ARF.
NOT PRETTY!!!!!! Especially when you HOG back on the elevator and the plane goes into a corkscrew loop.
Use a REVERSING Y-harnes!!!!! They cost $8.00. Thats right; eight bucks. If you can't afford $8.00, get outta the hobby. I don't mean to sound condescending or like a jerk.
Get the y-harnes with an adjustable pot and dial it in. Then "FUGETABOUTIT"
You'll be happier if you do.. No sense putting yourself through a headache for no reason.