The city that assesses the taxes also uses different formula to come up with a value.When I bought my commercial office building, a bank contracted someone to assess the value of the property.

This formula should give you the ratios to qualify for such a Loan.

The formula is that the tenant can spend 30% (sometimes 40% if their income is high) on housing.  

The formula for DSCR is: GSR/PITI.

I know many people look at this but it's a meaningless formula.

A cap rate is merely one lever in the value formula of: NOI/Cap rate = purchase price.

Either way, it's good to know what they do.Yes, it's great to learn how to estimate in detail, but in order to put a deal together when you're still learning, the formula may make things much easier. 

I am looking for a duplex or four Plex in town but unfortunately a lot of the prices don’t match with my current formula which tends to work well in Florida but not here right now.

If you find yourself traveling a great deal but housed/based in San Diego, one option outside the box you could consider is what they offer in a course called Bnb Formula. 

I do enjoy your formula, and will give it a go when assessing what areas I should be shopping around in.