That's 100% the truth ... for the OP , I have 120+ hosted SP20s that I've been mining if you want to try them out. Nothing like skipping DHL Customs 
Already have my waybills, but I appreciate the offer.
I'd simplify it even further and take the gamble and headache of difficulty/revenue out of the equation altogether by planning for a total Thash/s output
I do like simplifying things. But I want a good handle on all the unit economics before I start making things easy on myself. That's a great point though.
With my company, we used to break everything down to the cost per transaction. After a few years we realized that logic was flawed as our volume went up exponentially but other costs went up as well. Once we started concentrating on the unit economics of particular business lines, that's when we started making more money.
This is MUCH simpler math. There are only a few factors involved, which is wonderful. There also appears to be much more volatility. That part is also very different.
I've been researching the hell out of this. There seem to be a lot of opinions, based on the costs. Speculation on the market is an interesting factor to add in. This means I'm going to have to form my own opinion from experience ultimately. That's why we're starting with a 11 TH/s setup.