Rental Calc question

[Jay Helms]

#AskBP

So I have an opportunity on a mutli and playing around with the rental properties calc here on BP (unlimited usage is why I upgraded to Pro - worth it). 

All my #s stay the same but altering the income /expense yields different results. I want to reiterate all my inputs stay the same except for what's detailed below. Let me explain...

Option A: 

-- Monthly Income: $2,500

-- Monthly Expenses: $700

Yields a cash flow of $422.21 with a 12.84 return. 

In option B below, I net out the monthly income & expenses and get a different result. Here ya go:

Option B:

-- Monthly Income: $1,800

-- Monthly Expenses: $0.00( zero) 

This yields a better cash flow @ $541.21 with 16.46 return. 

In both options, the net monthly income is $1,800. My question is this, why is there a difference? What am I not understanding about this powerful tool?