I don't understand $ per door instead of % return

[Leigh Ann Smith]

I often hear investors refer to netting X dollars per door.  That makes no sense to me.  $200 per door per month might be great if you have 10K invested, but terrible if you have $100K invested.  Why does $ per door have any relevance at all?

[Matt Devincenzo]

It matters because just as in your example $200/door for a 100K investment isn't good, neither is a 12% return on $5,000 which is only $50/mo. That IMO is not worth the necessary work required of managing a rental...or PM whichever the case. 

They are two separate metrics that paint a different perspective on the same picture and then you can make a better decision.