This skill can be cast while facing away from a target; your character will about-face to face the target. However, if your character is facing away from the target before casting and you move your character after starting the channel, the skill will continue to channel but do nothing upon completion. This is true even if you’re within 600, the range of the skill.
Two ways I see to fix this:
Cause movement away from the target to cancel the skill and put it on a 4s CD.
For the sake of consistency with Life Siphon, allow the skill to channel successfully even while facing away from target.