Depth of Field Version 2

OK I think I have it. Theory:
The bigger the Print the bigger the depth of field, and the smaller the film format (negative size) the larger the depth of field.
The Smaller the Print the smaller the depth of field, and the bigger the film format (negative size) the smaller the depth of field.

I've combined both my Circle of Confusion calculations with Depth of Field Calculator Applet and think I have something useful.