If the current gen motion sensors can 'see' 90 degrees to the right and left...

Wall to wall in a non corner position would require 180 degrees.  But there's nothing saying you can't try it and see if it works for you.  Run the system in  test mode and see how it does.

Hmm.  I guess when the box said 90 degrees to the left and right I misread it then.  I'll test.

Looks like you're right.  It's 45 degrees to the right and 45 degrees to the left for a total of 90 degrees.