Need Help: What does it mean when my Cash-on-Cash percentage is lower than my Cap Rate?

[Michael Krassos]

Stay away I imagine, but seriously I'm analyzing a deal and want to make sure I understand what is happening.

It's a 2-family to buy and hold for $400,000, will put down 25%, so mortgage at $300,000.
Income is $45,600/Year
Expenses is $24,680(Taxes, Insurance, Utilities, reserves for vacancies and repair)
So NOI is $20,920.

After Mortgage is paid I have a seamingly attractive Cash Flow of $355, that's $177.45 per door!!

After factoring in my Cost to Purchase of $4838....

My cap rate is at 6.15% (I consider okay for NJ and condition of property), and my CoC is 4.74%!

What's is happening? Why is the CoC lower than my Cap Rate? Is this a deal or not?