The Executioner's Second Phase

(If you want clarification on what I mean by The Executioner, click here -- spoilers at your own risk):

Spoiler

The powered-up Aledar fight in A Hunter's Calling that happens if you kill Tasim first

For both The Executioner and The Protector, when they enter their second phase, they gain the ability to deal a heavy amount of damage. In the case of The Protector, it's a heavily telegraphed nuclear bomb that can be easily avoided by standing at the corners. However, for the Executioner, it's a swath of flames that covers the entire arena that does less damage than the bomb. This wouldn't be much of a problem on its own, but I can't seem to find a way to actually avoid it. As a result, I either end up dying or have to focus on activating life steal instead of actually damaging him. In the former case, I ended up killing the Betrayed first so I could fight the Protector instead (rip my hero beta assassin).

Is there a way to avoid The Executioner's special attack in his second phase?