There is no problem with putting the servos at the approx mid point. If there is then there are a lot of Hangar P-51 PTS's, Great Planes Escapades, Great Planes Ryan STA's, and Great Planes Super Skybolts that need to be re-engineered by the manufactures. All these have aileron servos at or near the aileron mid point. After flying some of them for years I have to say that they are all doing fine.