As it stands, this is the last achievement needed by my 10s for the Frostwyrms, save for Been Waiting (but that one is easy).
We have explored various options. What we are finding is the tanks, about 1m into the fight, hitting 6 stacks.
We originally used a dual iceblock placement setup as we did for normal and hard mode. We have subsequently gone to 3 iceblocks, one on the center of her front shoulder, one at the head and one in the center of her body. They roughly form a triangle, to ensure that all blocks are on the head end of the dragon. This alleviated the problem we had when tanks would need a black real fast but yet there was a new orb coming and that person was to be where the iceblock currently is. We are not breaking any one block the tank goes to until they call that they are clean. Tanks are also swapping the instant the prior tank is clean.
I don't need the 'tanks need to play better' comments. We have spend an hour on it so far, and I expected it to take a little bit.
I am just looking for feedback from others who have done it. Speculation isn't welcome.