The problem with the dragon is that it's hard to tell when it is and isn't on the poison patches that heal it.
Aiatar isn't directly healed by the pools, he gains a buff from them, it's this buff that heals him, easy to see if it's up or not, also his HP bar going in the direction you don't want it to.
Positioning Aiatar near the edge and having everyone else near the edges of the room or standing next to the poison pools while spread out a little helps to control placement, leaving the tank with plenty of manoeuvring room.
Also as a tank I've found it easier to stand inside Aiatars targeting ring, near his left front foot, can run through him to avoid poison breath.