Where did you get 4.3? I thought it was 3.94 rating equals 1 point of expertise; ~15.76 points is 1% decreased chance,
I didn't get it from here, though! I'll have to check the guides real fast...
EDIT: Yep, "Expertise ____________ 3.9 to 1" by Ciderhelm - My numbers are a bit more precise, but the game will round them so then it makes sense.
I can also substantiate that Moro 'seems' MUCH more steady now. My wife, who is always my main healer after our Moro kill commented that she never worried about me. I was using neck, bracers, and mallet. Good stuff. I think the era of waking up in a cold sweat, terrified of being effectively one-shot by Moro, is over!
Personally, I think it's the best neck in the game.