TLDR;The main issue seems to stem from the original equation. I think you are using the duration property in your equation as a time between factor... instead of the end date.
Not totally sure on how I'd do it for a Monthly breakdown, but.
You can do a Revenue per Day calucation all in one calculated property if you cofigure it as below swapping out your appropriate properties. Be sure the Output type is set to Number and formatted to Currency.