Talk:Ember/@comment-172.15.16.99-20151104152411/@comment-8256051-20151121114923

The actual formula for total draining cost is (2-efficiency)/duration

So basically if you have 190% efficiency and 40+% duration, you'll have maximum efficiency out of all your abilities (other combinations are possible, but a bit tougher to achieve).

Quick example : with Fleeting Expertise, Streamline, Intensify, Transient Fortitude and Constitution, World on Fire will cost 12.5 to cast and 0.75 energy per second to maintain with 185% strength, 175%(190%) efficiency and 40.5% duration.

I explained it in details here