Presume stop is not going backwards.
When stop allowed but no reversing if you watched where somebody started hopping from and then where they finished up they could of gone back a few inches but you could never tell at which point they actually went back but they did -5's were hardly ever given.
Also I found you had to use more markers and tape to stop riders splitting sections into sevral zones each being attempted at odd angles of attack rather than a straightforward route through the planned section.
As said already the simple answer is that there isn't one!!