Cash on cash return: new mystery of the underwriting cosmos discovered?

[Benjamin Aaker]

Calling all you data nerds out there to help me. Looking at you Data Deli @Dave Meyer. I've been doing a deep dive looking at cash on cash return for various down payments and expenses on properties with a mortgage. If expenses are high relative to income, the cash on cash increases when the down payment increases (16k column). If expenses are low relative to income, the cash on cash decreases when down payment increases (10k column).

There must be an inflection point somewhere, so I did some spreadsheeting and indeed there is a point where the expenses and income are such that the cash on cash return is the same for all given down payments!

Have I just discovered the secret to getting rich in real estate? Have I made a terrible mathematical error? What mystery of the universe is uncovered here? And how can we use this when underwriting our deals? Surely someone has noticed this before and can explain it.