Overall Width of Back of Mounting Bracket for Arlo Video Doorbell

[Embeeous]

I'm waiting on the arrival of my new Arlo Video Doorbell, and I just rechecked the specs.  The overall width of the doorbell is 1.7" and I've got 1.5" of total space to play with, unless I start cutting door steel and molding to make it fit.  The width increases to unlimited just a fraction of an inch out from the door, but right where it would mount, it's 1.5", with brick on one side and steel on the other. However, when I look closely at the mounting bracket for the doorbell, the overall width at the back where it mounts is less than the overall width of the bracket closer to where the doorbell snaps in.  So I'm thinking that this might actually fit, or it's going to be real close.  Does anyone know what that width of the mounting bracket is on the back end where it mounts up against the wall? Thanks in advance for your assistance.