are you talking about the servo horns the pieces that connect the servo to the rod? they should all be horizontal when the swashplate is at midway point of its travel. if one servo arm is higher than the other, this will cause a difference in distance traveled because as you can see there is a bit of an arc on the servo arm when it moves, so you have to make sure all 3 servo horns are at the same exact height when the swashplate is level.