@Sundeep Amin
I am in San Diego and specialize in Escondido.
The cap expense I use is $300/month for SFR of standard rental size (think 800' - 1100': 2 or 3 BR, 2 BA or less) and $250/month attached. I derived this number with a cap expense sheet that I bound on BP and replacing the numbers with my expected costs (higher than elsewhere) and my experienced life span (My experienced life range varied significantly from other projections: for example sliding aluminum windows I experienced a shorter life than the work sheet, similar for HVACs. I do not base cap expense on rent because the correlation is weak. If I have a 1120' 3/2 rent at $2500 and a 4/2 1450' at $1900 (BTW these are 2 of my units and the $1900 is a close to market rent) which is likely to have greater cap expense? I believe the larger 4/2 is likely to have higher cap expense.
I typically start with 75 to 80% LTV (the lenders typically want 75% LTV so finding greater than 75% LTV is more work). I attempt to keep my equity as low as I can but sometimes it gets a little high (I have a few units were for various reasons my equity is above 50% of value which is not leveraging the money well).
Here is what I use for my cash flow numbers: Rent - Mortgage - Escrow (tax and insurance) - Cap expense (see above) - 10% rent (maintenance and vacancy: I actually have so far experienced less than 10% for vacancies and maintenance but I have a cheap dedicated maintenance person and take good care of our tenants) - incidentals (I have 3 units that I provide gardener and 2 units that I pay water/trash). Ideally this results in a positive number. If it does not I also look at the return if I include the principle from the payment. Note when the interest rates are low the principle from the payment can be substantial (I have one property were the principle form payment is >$500/month and a couple of others at >$400/month. This principle gain is net worth gain but obtaining it is similar to obtaining appreciation (i.e. requires a refinance or ELOC) so is not as desirable as cash flow not a result of principle gain.
As for purchases in San Diego: It is real difficult to find a cash flowing SFR using my numbers. Multiplexes in select areas of San Diego will often cash flow but not like other parts of the country. Where traditionally money is made in San Diego by buy n hold is in appreciation and rent appreciation. I have purchased properties that did not cash flow using my formula when purchased but I believe my last property to not cash flow will cash flow next month (rent appreciation) but where I have made most of my REI money is on the property appreciation.
Escondido has been a very good market for me. I recently refinanced a few of my properties and took out all of my initial investment. So I have no money currently in on those properties and yet they have equity and are cash flowing (one is soon to be cash flowing).
Hopefully this answers many of your questions including if investors are including all expenses (they should be) and how investors are making money on buy n hold in San Diego.
Good luck.