There's no need to overcomplicate things, the theory works fine as it is.
If you're going to try and move past a fighter in close proximity, and he chooses to try and stop you, there's most likely gonna be repercussions.
The only problem I can see is with the movement cancel and when that occurs. If the coding isn't right it could be a bit buggy or jerky.
I *think* this is how it's going to work
Let's say the Fighter in your way, you have 10 metres of in game space to move through a corridor. Fighter's engagement area is 5 metres of ingame space.
You issue a move action to behind the fighter with a character.
a) Pathfinding - if there is a gap between the moveable area and the fighter's engagement area - will your character automatically try and avoid the engagement area or will it just walk the most direct route through the corridor.
b) The Fighter's AI: Whether he moves to attack the nearest character.
If the AI fighter essentially "clicks on you" or engages the character that you issue the move command to, once the character enters the fighter's engagement area, that character's movement action is cancelled and as Sawyer said, there's some kind of connect between selection circles and an icon on the character portrait or something to signal that that character is now engaged in melee combat.
If you issue another move command to exit the engagement area, the fighter get's an attack of opportunity with a bonus against that character, and if it hit's it stops the movement action of that character and some kind of animation is triggered.
A question I can think of regarding that:
If you issue another move command shortly after, once the animation has finished, and the fighter is still engaging you, does he get another free attack ?
You could potentially use a rogue or a barbarian, who appear to be 'skilled' at breaking engagement with melee characters to bait a character away from a corridor so the rest of your party can move through, as long as you don't move another character nearby while doing so so that their target priority changes. Totally depends on encounter design though.
Edited by Sensuki, 05 March 2013 - 06:11 PM.