There's a lot of movement on that encounter, and I tend to get poked in the back occasionally. Data for avoidance on Freya is going to be sketchy... though misses should be omnidirectional, so that shouldn't be effected. I net lose defense and the SSG rune (and thus miss chance), it's just raw dodge/parry that go up. I'm guessing the miss difference there is pure RNG. EDIT: Oh, you meant total avoidance, not pure miss. Yeah - a big factor there is going to be hits in the back while repositioning. Usually, "run like hell and get away from the raid with Nature's Fury" is less total damage done than backing/strafing slowly away to ensure she's in front of me. So it's not random, I may have just had better facing last night. 62% avoidance is about right for my gear, 54.3% is low. That said, it should statistically have increased - just that it's hard to measure how much of that increase was better play and how much was the weapon change. I wouldn't throw it out completely, but I would caveat any observations on avoidance in that encounter.
Anyway, glad I could help. The Vezax results should be pure (it's just a really long tank and spank from my end, which is perfect for this) and back the math I'd done back before WotLK even hit. The only consideration would be using an avoidance 2h such as ID or Rune Edge to bump up 2h avoidance by another 1-2%, but even then it should be a very small gain.