yeah, it's not like a video game. The mic hears what the mic hears. Alexa ESP decides which Mic has the best sound and chooses that Echo as the one that heard you.
I've got Echo-Something in every room of the house, and here in my office, the ring will light up as it decides when I faintly hear my wife starting a command in the living room, which is around several corners and 30+ feet away
The two issues I have with the wrong one picking up is the living room and kitchen. I've stood at the stove, looking at the Show next to me while I'm trying to set a timer and the living room picks it up. Makes no sense.
The other issue is followup mode. starting a command and stopping, or trying to give a second "normal" command. Because the first one is busy sending the first command, the other unit hears the second and takes priority. Not exactly described, but there's some wonkiness you can get into by messing up a command or trying to talk over her.