Historically, the carbine was not fired from the mounted position. It was designed for dismounted use, so holding it ready to dismount would be more accurate (but less impressive on table ;-). In the event that contact was made during scouting, either the troop would back off or would charge with lance or sword, depending on how close the terrain was. The options depended on whether it was important to preserve operational secrecy or not. There were occasions when a troop or troopers would dismount and engage with carbines when scouting.
Robert