Originally Posted by
Kae
I believe this is how it works, but I do agree it's a very obtuse and misleading ability. The tooltip (viewable on wowhead or the dungeon journal) is confusing as fuck and doesn't help matters.
I'm pretty sure as long as the rest of the raid is away from the tanks they're safe. The tanks themselves need to wait until the cast -starts- before moving and then get as far away from where they were when it started as possible. Always using some kind of mitigation is also very important though, because with 2 debuffs from the boss even being 20 yards out can hurt like fuck.
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It's definitely based on position of the tanks and not how close the raid is to the boss. Otherwise, melee would have to move out of melee range every time Slam comes or they'd get utterly one-shot. But they don't, the damage the rest of the raid takes is based on distance from the tanks and not the boss.