Hi Steven, welcome to the community!
Very kind of you to work that up and share it with us. Like you, several users have come up with solutions for that use case, but many of us, myself included have opted for a simple sight gauge shared by @dwardio … No Math Focus Ruler
With the crumb tray out, open the front door so you can sight across the surface of the material and shim it until it is between the marks. The lens has the ability to move 1/2" for autofocus, so anywhere between the marks works.
Thanks for joining us. 