If its that tight and there is another pilot trying to jumpseat wouldn't you take the positive space seat anyway so that the other pilot can get home or to work? Or do you not get positive space for deadhead? On ASA we have priority, then mainline has priority over other connection carriers, then other connection carriers, and then first come for the rest. But I think within the last 20 minutes of a flight it is first come first serve, at least that's how it is on Delta mainline.