cash-on-cash return (duplex vs apartment bldg)

[Todd Norris]

I have several small multi-family properties, and the cash on cash % return in my area (Northern Indiana) hovers around 20%. I'm thinking of taking the plunge into larger (50+ unit) apartment buildings/complexes. As a general rule, is the cash on cash % return higher or lower for a 50+ apartment complex than a duplex?

I know that every property is different, but I have found the 20% cash on cash % return figure to be a pretty good indicator of a good duplex. Apartment buildings seem to be all over the place...even in the same market. 

Thoughts?