Overlords
Overlords move to random region center.
Limit appears to be the neighbor of a region that contains a building or creep?
Overlords will move to the location a cloaked enemy has attacked.
Air units will always travel to the center of a region, with the exception of targetting a unit.
Observers
Occasionally follow a powerful enemy like an Archon.
Bunkers
Bunker's top left placed at the closest point to the center of a choke region.
Shot of enemies gathering in the center of a region that is 3-4 regions away from the enemy base. (2 regions from enemy's choke)