I'm not here to argue about what your justification should or shouldn't be.  Just talking through my own thoughts and how I may justify differently.

I have two rigs running a total of around 390mh/s and let's say roughly 1.65kw.  As such, I pay around $6 a day to run this @$.15US per kwh.

Notwithstanding hardware cost, which obviously is a concern, but on a power basis I would need to clear out that $6 a day in ETH or more basically at today's price.  If I don't, it would be more cost effective to just buy the ETH directly.  I should also add that it would be $6/day + one's tax bracket, but I digress...

$6/390=0.015 USD per day per MH.

You can pop over to https://bitinfocharts.com/comparison/ethereum-mining_profitability.html#6m to view just this metric.  Currently it's like around 0.03, and it has indeed been above that threshold for a bit of time, at times substantially.  **The rewards does not always follow when ETH or whatever coin is hot, just whether the network is paying at a given moment.  Recently the reward was 2x what it is today, but ETH price wasn't 2x, it was maybe 10% higher than it is now.  

YMMV, but point of discussion, hope you don't mind.  

Also, if I'm understanding right you have like an order of magnitude or two more hash rate than I do, so different metric prevails.