Do use the hole closest to the servo screw you can , as this allows the servo to keep its pot clean ,by increasing the full extent of the servos travel at the pot
That will give you a --better feel --on the sticks as the total travel is the same ,but the travel moves more slowly through the sticks curve
You may just be damaging the balsa that is located under the horn, after a given number of flights
The balsa is often crushed by the horn ,at installation
I pin hole the balsa under the horn ,use Ca ,and a piece of 1/16 ply on top and bottom of that and then install the horn
Slack that developes between the clevis pin and the horn ,has to be inspected at intervals
Any slack from the servo arm ,to the horn ,will increase itself ,all must be snug
Hayes clevis' s are my choice
Use the red sullivan rods ,with the metal pushrod for the most flex free ,direct connection possible
A fly on rails ,feel
They MUST be secured to the inside of the fuse ,about mid way thru the inside of the fiuse ,to prevent the red sleeve from flexing ,when the wind is pushing on the elevator
Only my best guess , as this is an odd thing to be happening to more than one airframe ,with a radio having been changed