With the setUnitPos command, you can make an AI remain in one of three stances, standing, crouched and prone. But it would also be useful to limit the stances available to an AI.
I suggest a new command which would let the mission designer prevent the AI from using a certain stance, or stances. Examples:
unit1 allowUnitPos ["UP", "MIDDLE"]; -- allows the unit to stand and crouch, but not go prone.
unit1 disableUnitPos "DOWN"; -- singular version of the command just disabling the prone stance.