So... I had a problem with an AI. I fixed it, but now... I still have the same problem with the AI.
PROBLEM:
-Set AI to approach "closest" enemy base which is being approached by an enemy.
-Enemy AI has one of their bots start moving toward the base nearest to my units while another unit is capturing.
-This prompts any units not already close enough to attack to retreat toward the base behind them instead of attacking the one the enemy is trying to capture at.
SOLUTION:
-Change AI to approach "closest to resource" enemy base with otherwise same properties.
BUG:
-In spite of the AI change, the units display the same behaviour.
-The enemy base closest to a resource is NOT the base being targeted for the move action.
I ended up having to use alternative conditions (unrelated to bases) to get the AI to behave as intended.