A unit is on the flank of an enemy unit and has the enemy unit in its zone of control. My question is what movement options has the enemy unit got being in this zone of control. Can it move forward, turn to face or does it just have to stand its ground ?.

in a few minutes the updated version of Basic Impetus will be online

here the new text

5.5 ZONE OF CONTROL
Every Unit, not disordered and not in melee, has a Zone of Control that corresponds to a rectangular area that has its’ base as the front of the Unit and a short side of 5U. You may not wheel, move sideways, at an angle if you are in an enemy Zone of Control. The only moves allowed within an enemy Zone of Control are:
1) Move in a straight line directly towards the enemy unit exerting the Zone of Control.
2) Move directly to the rear.
The only exception to this is when the Unit exerting the Zone of Control is not to the front of the unit. In this case a Unit that is NOT in disorder may move straight ahead but this movement will result in Disorder.