In order to get the full range out of your servo's, they must be installed in such a way that the entire servo range will map on the entire throw of the Ailerons. This means that you must have equal throw around the center of the servos.

This is the normal situation if you have only one aileron servo, or an Y-cable with two aileron servos in a mirrored setup, or a tail-mixer y-cable with two servos in a parallel setup. 

This is shown in the next image, where we used a 'top drive' servo linkage:

If you have a 'normal' servo install, with the control horns on the bottom side of the aileron, the situation is exactly the same. It may only be that you have to inverse the servo direction. That means that -100% will become 100% and vice versa.

We have used the term 'travel' to refer to the % of maximum throw that you want on a certain control surface, such as flaps or ailerons. They are always relative to the max throw.

If you have two separate servos, and enough channels on your transmitter/receiver, you might consider setting the ailerons up as flaperons.