If you look at some of the 428 Q-500 aircraft, they have wide chord ailerons that are short. Also set closer to the root of the wing than the tip. The wide chord gives better slow speed aileron effectiveness by increasing aileron area. Being inboard helps with flutter issues.
My recommendation would have been to do this and also move the servo to be centered on the aileron.
Just for anyone else, If the ailerons are going all the way out to the tip, one other trick is to taper the aileron at the wing tip to eliminate the vortex effect on the T.E. of the aileron. This works well. Also, stiff aileron material needs to be used to start with as light, flexible ailerons are prone to flutter.
Congratulations on solving your problem.