After doing Titan HM I want to clarify some of the ways things work.

Do NOT cast while moving. This is the big thing. Melee is the same way. If you melee right before you leave the circle, it will register you in the circle prior to the explosion.

So if I true Thrust into HM Titan while the animation is expiring and I did it when i was still in there, I will stil take damage even though I left.

Also, you do have to move really fast. It is a reaction thing, and you need to take great steps, not small ones. Get out the way and you will be fine.