Finer Points of Necro Feign Death

[Axoc]

So I think I'm actually starting to learn to play Necromancer correctly, and it's tons of fun. I've got this issue with FD though. It seems to work 60-80% of the time, which is for sure helpful, but whenever it doesn't work and I get hit by a mob, I seem to get stuck for an unusually long amount of time. This has caused two deaths over the past three hours. The chat window doesn't say that I've been stunned, but I'm stuck standing there having been freshly knocked out of FD.

Is there any way to increase my chance of FD working versus a mob? Is MR tied to this? Also how do I avoid this god awful stun that is longer than a stun that happens whenever I get attacked while FD'ed?