G'day Mate,
If you have a lot of subtrim, on either of the servos, they will be out of centre, on the monitor.
Get the servos centred mechanically, with NO subtrim, so that each aileron pushrod is as close to 90 degrees as possible to the servo arm, then use subtrim to adjust.
Keep the amount of subtrim to a minimum, & you will have more throw.
BUT be aware, if you set up your servos, & use some subtrim, make sure they are moving in the correct direction, because if you reverse them the subtrim will have moved the centre, the wrong way.