This is with Celestial Fire melee, and it seems the first fireball is the most reliable with a ~90% success, while second and third just have diminishing returns after that (~40% - ~10-5%) Let me know from the poll if it works for other CF users please. Edit: On further testing, it seems that less distance to the target makes it more consistent, but it is still only around 40% of my procs that work, on a red bar that i'm leveled against.