So when you have an arriving aircraft and an aircraft attempting to depart, the general rule is that if the inbound aircraft is within two miles of the threshold then the departing aircraft is to hold short of the runway until the inbound one has landed. At this point there isn’t enough time for the departing aircraft to clear the runway.
As it has been stated numerous times, the distance that an aircraft appears in tower view and on radar is in relation to the tower itself, not the runway threshold.
I believe it would be a good idea (at least on the TS) to have marks on a controller’s radar that mark the two mile final point on the extended centerline of each runway. In theory, it would look something like this:
Notice that on parallel runways that are offset the two mile mark is separate for each runway and on parallel runways that are not offset the line continues between the two runways.