I think an example would be best for this:
Lets say I have option A a property where the loan is $100,000. The rent is $2,000/month because we live in perfect land. Using the 50% rule:
Expenses: $1000 per month
Loan (minus taxes and insurance cause I don't know that) @ 30 years for 7.25%: 682.17
Profit: $317.83 (this is a SFR)
Now, in corner B we have a $1,300,000 property. It has x amount of units generating a gross monthly income of $26,000.
Expenses: $13,000
Loan for the same term and finance rate: $8,868.29
Profit: $4,131.71
Now, is that accurate? The major difference in these examples is that I can't cover the $8,868.29 mortgage with my salary. I also don't know insurance and tax costs. The loans are secured by the property value. Let's say option A's true value is $120,000 and option B's value is $1,450,00 for sake of securing a loan at 80-90% of the property's value. The loan would include closing costs, ect because I have a great lender (again, all speculative).