https://www.investopedia.com/ask/answers/060415/what-average-annual-return-typical-long-term-investment-real-estate-sector.asp

https://www.trulia.com/real_estate/Los_Angeles-California/market-trends/

Rental income -(mortgage interest + insurance + repair + property tax) = gain (return) from  payment = G(x)

G(X) / purchase cost = Annual Gn %

Gn% + 5% = annual rate of return of property in Los Angeles 

 The only controllable expense is mortgage expenses, if  you have put down more cash, less mortgage interest, then you have higher Gn%