Alexa is weird this way. It has the ability to assign things to certain areas, it's just hard to figure out how to make it happen. For example, I have Alexa controlled lights in my basement and it knows what to turn on when I say "Turn on the lights" while in my basement. I also have Alexa controlled lights in my garage, and until recently I specifically had to tell it "Turn on the garage lights" while standing in my garage. However, I made a change recently (I can't remember what it was) and now my garage auto-magically knows that I'm talking about it's lights while I'm in the garage.
So, I think Alexa has the ability to know which A/C unit your talking about while standing in the room, but it's not clear how to make it happen. Also, it sometimes stops working, even after you have it configured correctly; that's the real frustrating part!