Good question.
If you do a master slave relation between the two servos and run a synchronization, the slave will adjust to compensate for its differences in linkage etc. If you go back in and then remove the bond by selecting it to be a single servo again, it will retain the created curve. Now you should be careful when you go in and edit the curve. You should only move it as whole curve with the move curve button to adjust the servo center point. which should now be at the same spot as the spot for the elevator setup. Notice that any trim necessary for aileron will of course throw a wrench in. Any adjustments should always be done with aileron trim set to zero. Let me know how it works for you.

Another tip on how to use curves that you don't want to create over and over again. you can simply use the Master - slave relationship to transfer the curve from one servo to another. You can transfer it to an unused servo outlet and break the bondage afterwards. Now you can store this curve or even more others this way and create your own catalog of curves and transfer them by linking a master slave relation and after releasing them, you still have the curve in there.

thanks

Gerhard