Zone
When a transporter gives up the zone behind it, relative to entering the next one.
The choice decides how closely transporters may follow one another, and so how much of the guide path a fleet can use at once. It is a modelling parameter, not an implementation detail: the control system of a real installation implements one of these, and which one it implements changes throughput.
Inheritors
Types
Give up the zone behind after travelling the given distance into the next one: the general case, with the other two as its endpoints.
Give up the zone behind only on arriving in the next one, keeping a follower a full zone further back. The greater separation, and the default.
Give up the zone behind at the instant travel into the next one begins, so that a following transporter may claim it immediately. The closest following.