High vs low value rentals

[Jonathan Lucas]

I hope this makes sense, here goes:
I was doing some math on properties locally available for rent in joplin, mo. I recorded information on each individual property, put the address in zillow to find the purchase price of similar properties, figured mortgage payments, taxes, and insurance, and got a rough estimate of cash flow.
What struck me is how much lower the ROI (based on rent charged) was for the higher rent properties. Also, properties with half the value were producing similar amounts of cashflow.
The only reason I can figure is A. My numbers were wrong, or B. the higher priced properties are more valuable for their resale price than their cashflow value.
Any thoughts on this?
Thanks!