I would use 2 triggers for this type of thing. First, a detection trigger. If the units in the base are west, you'd make a trigger that extends a good distance beyond the base of type- East, detected by west. In the on activation put- detected=true. Next, make another trigger that covers just the base of type, west, present, and in the condition put detected. In the on activation you'd put-
aware = "AWARE"; "_x setbehaviour aware" foreach thislist
That should change all the west soldiers in the base to aware behaviour. This is an easy way to change behaviour for multiple groups. It can also be done by synchronizing waypoints with the detection trigger if you only have 1 or 2 groups. There's almost always several ways to do things with this game.