Hi!
Sorry ! But you are wrong!
The reason for having the servo arm as short as possible is that the gear sloop in the gear box inside the servo will be minimized that way. Test by mounting a long servo arm (around 30mm long) on the servo and notice how much play you get at the tip of the arm. Then take a short servo arm (around 10mm long) and do the same test.
On my pylon racers where the elevator throw is around 3mm up and 3mm down measured at the trailing edge of the elevator I have the linkage mounted on the servo arm approx 7-10mm from the servo center. The result is an elevator without any flex at all.
The opposite is when it comes to the control surface, here we want to have as long control arm as possible to reduce the play in the linkage and hinges (the closer you put the linkage to the hinge line the more play you build in)
Remember that the balance of he plane (C of G) is involved too in setting up an airplane and the rule of thumb here is to balance the plane as far back as is possible and at the same time have the servo arm as short as possible and the control arm as long as possible. Of coarse there is a limit to how far back you can have the C of G but this you have to find by trail and error! A little nose heavy first then move servos and batteries rearward until you find the "sweet spot".
This is the rule of thumb when it comes to setting up any airplane!
