This is my mistake. What I meant was that for most people damage multiplier is just that, the multiplier. When you ask some one what is the damage multiplier of 100% ED, they will say 2x. If you ask someone what is the multiplier of 200% ED, they will say 3x. Only when you ask them what is the ratio of the 2, will they answer 1.5x. A ratio (MI%) is not a multiplier but a comparison between the different values. For us math users, they are equivalant since we are comparing the multiplier of the extra affix. But for a normal person, it gets confusing.
What I am asking here is for more information on the example. You explained that you were using Druidic for Poison DoT calculation and why Regeneration over Crytal MP Regen but no mention on why Cosmic Power over things like Equality/Plague. I can figure out the answer, but a normal reader might get confused since you are so detailed in explaining your other choices but not this one.