More down than up aileron travel is very seldom used on either high or low wing airplanes. High wing airplanes frequently display a greater need for aileron differential (more up than down) than do their low wing brethren, simply because the high wing configuration tends to produce more yaw/roll coupling, and high wing models are seldom used for precision aerobatics, where aileron differential can produce unwelcome roll/pitch coupling - a downside of aileron differential.