Demon6324236,

What do all of those monsters have in common?

Eph suffers the same fate as nearly every other add effect weapon in the game, vs anything above your level it's proc rate and effectiveness rapidly diminishes, especially on NMs. It's SE's way of being stupid, they give it a powerful effect with a lowish proc rate but then nerf the sh!t out of it on any remotely dangerous to maintain "barance". Better to have a weaker effect that consistently procs (wind knife off that bird) then to have one that fluctuates and is rendered useless on hard stuff.

The reason it gets ignored is that on anything worth fighting it won't be a factor.