Sounds like those mirrors are new to the american driver....they are standard on every car in europe. I love them! I drove a Edge for the last years and it had some kind of light inside the mirror that came on when there was a car in the blind spot and i hated those so much.
Just adjust the mirrors like you would adjust every other car mirror and it will always show you the blind spot.
I dont understand how people cant like them. :-)
my 2011 Edge has the blind spot monitoring as you describe and i MUCH prefer the actual mirrors like on the mustang. i've contemplated buying small blind spot mirrors to put on and then not deal with the light.