So that I understand.

The rear d will work as long as I am not in 53/25/23/21/20 or 39/12/13/14/15.

I can see it not working in 53/25/23 or 39/12/13 but the others shouldn't be a problem 'cause that's how I shift now. Basically once I hit the middle of the cassette it's time to go to the big ring.