ORIGINAL: rjh1971
Yes I think we would have to distinguish between stumbling upon an enemy when advancing using all the AP and ending adjacent to an enemy unit. But given the actual game mechanics if ending adjacent wouldn't trigger the surprise attack then we would never have surprise attacks because everybody is going to move hex by hex.
You've hit the nail on the head! If moving hex by hex didn't have any penalty, then we'd always move one hex at a time.
The rules are as follows:
Unit Spotting Ranges During Movement
If a unit has moved its full distance in one move, i.e. without being deselected at any point, then its full spotting range will remain after its movement. However, by moving its full movement all at once the risk of Surprise Encounters with hidden enemy units is high.
The only way to avoid these Surprise Encounters is either to reconnoiter with aircraft first, or to deselect an advancing unit, have it spot, and then move it again.
But when a unit moves or attacks, after its second committed move (i.e. when it has been deselected a second time) its spotting range is reduced to 1 hex. Thus it retains its full spotting range after its first move, but loses it once it moves a second time.
The unit's movement range will update as it is moved, and you can click on new attainable destination hexes without deselecting it.