Source: BIKI: setWaypointCompletionRadius
While the descriptions says:
The completion radius allows units to call the waypoint completed once they are inside of the given circle.
However the note at the end tells more truth about it:
So far setWaypointCompletionRadius seems to do nothing for my infantry only group + AI only group +...
The way it works now (is that) it is (set) complete(d) once (the) unit is inside (the radius) and
does not think it would be reasonable to move any closer (to the exact waypoint position).
single unit group to be precise.
Any ideas to make them also complete their MOVE waypoint when close enough?
(aka inside the completion radius)