Thanks, Arumat.

Allow me to paraphrase using my own example, just to make sure I follow.

Sleep has 3 minute cooldown. The cooldown counter begins @ my first cast. During this cooldown period, I further sleep the mob at reduced effectiveness @ 50% duration, then again @ 25% duration. Any additional casting until cooldown is achieved will be fully resisted. Now, the 3 minute cooldown is complete. I sleep the mob again, is the '*' footnote saying my first sleep after cooldown will land @ 25%? I think that's what you're telling me. Regards.