There is a bug with the cooldown reduction of this trait. It doesnt work when a skill gets interrupted (e.g. siphon life channel goes to 12 sec cd instead of 8 sec cd) even if you are above the health threshold (also when the cd reduction should work).
This is doesnt happen with more normal cooldown reduction traits like unholy favor (the axe one) and ghostly claws (the channeled skills are a good way to see that since normal skills go on the 4 sec interrupt cooldown). Hence why i think it is a bug.
My guess on how the trait works that it only checks the threshold requirments and applies the cooldown reduction when the cast is successful. However it should also check when the cast is interrupted.