You'll have a few options once they move out; you can increase the rent to cover the difference, have the studio metered separately or write a clause into your lease that they pay either a portion of electricity or that they pay 100% over a predetermined amount.

It's grabbing a few data points and building a pre-determined narrative with selective data.

If you are valuating SFR's focus on  other long-term plays like debt pay-down, equity, and tax benefits...Not discouraging your valuation..practice helps...but your vacancy loss is pre-determined as a component of GOI...it's not an operating expense...and capital expenditures are what they are...again, not an operating expense (and 15% may be excessive...).PM me or feed me a couple of your property addresses and financials and I'd be glad to help you sort these out. 

Can be 50/50, 60/40 or a predetermined amount such as $500 or more.The simple answer to your question about how does the investor make money. 

Today Many electric utilities have graded service rates to encourage efficiency and bill you at a higher per KW rate once you reach predetermined consumption thresholds.Likewise, some ISPs will bill you at a higher rate when you go over your package data threshold.If your ISP is blocking your traffic when you reach a threshold it's an indication they are infrastructure constrained - or "business constrained" - and you should be looking for a different provider.

I think a lot of people look at the topic from a fixed/predetermined mindset.

I personally think entering into an agreement to buy without predetermined means is highly unethical.  

We set it up so that when the vent fan is turned off it stays on for a predetermined time before shutting off.

A mortgage pre-determines even payments so that principal+interest pays the loan off in a specific amount of time.