Big-S elevons 1 and 2, when deflecting, creates excessive drag, specially on high speeds. During pitch maneuvers the craft only looses a bit of speed, but during roll maneuvers, depending of angle of attack, one side creates a lot of drag, forcing the craft to yaw, causing partial to complete loss of control, specially during reentry... Some control surfaces suffer from this but in a lesser manner, some others don't create drag when deflected... I suggest to not remove the drag from those parts, but instead, make possible to set how much it deflects. This way we can still use this parts as airbreaks and flaps, which needs drag to work...