hmmm.. from what i'm readying, you guys are only assuming this block arrows ONLY. But if you read it again it says magical projectiles which can almost never miss unless you side-step them.
It was 75%...I wonder why they changed it back to 50%...considering the long recharge time I only used that skill once - versus the dopple gangler with my ele (since he was Ele that was proficiend with bow).