If the stated Board Controlled movement "Move Toward" says "closest opposing unit" then the AI unit will make an attempt to move even if its more than a single move away.
Sometimes the movement rule state that the unit won't move if they cannot improve their position, as is the case for Zipa and Zaque. In that case they will only move if that move would bring it closer to the opposing unit.
Note, that you always try to fulfill the first condition first, "closest opposing unit", and only if there is a tie on this first condition (i.e. two or more closest units) you move on to the second condition "weakest opposing unit". If there is still a tie players choose.