IME checkrides are normally flown in the right seat, but can be in the left. I've done checkrides with the check pilot in the jumpseat, and the crew being checked in the front seats, with no particular requirement, it's up the to crew to decide where they will sit. In normal operations, the crew changes seats regularly, often swapping each day, sometimes on other schedules, as mutually agreed. As a captain I really preferred the left seat if the weather was going to be a big factor, because I would rather let the cojo fly while I watch him/her, instead of having to concentrate on flying the machine. In any case, in the US it's a moot point, as there is no regulation concerning who must be in what seat.