Already answered by MOT in the Miniatures Game forum.
I know this one. Combat VS a unit in the same hex (DF, Close Assault, etc) does not require line of sight “into”, “out of” or “through” its hex. So for vehlce VS vehicle DF, the only way to draw DF is to go through hex the other vehicle is in. The defender can opt to perform the DF while the Mover is in the same hex, though obvioulsy if it succeeds then the Mover has to trace his path back to the first legal resting position.