What Sandor means is use as much of the available servo travel as you can & vary the horn length & hole position on the servo to get close to the needed flap movement. 

It's the same as short or long servo arms, it's easier to stall a servo if it has long arms on it so keep them short.

Likewise it's easier to move a control surface with longer horns on them so keep them long. 

By increasing the servo travel you can make the servo arms shorter & the flap horns longer. - John.