Weird. You just changed this file and my comment went away.  The comment said: please add a comment documenting what this constant does and what units it is measured in.
I see now that this is in the camera coordinate system.  Please also document why you're using the value you are using.

A radius of 20 out of 2000 means that the focus area will occupy just 1/50th of the width and height of the screen which, I suspect is way to small to have anything to focus on.  There should presumably be some relationship between this value and the radius of the focus ring that is displayed on the screen.