Well I'm glad you asked :)

The delegations/powerdowns only relate to the Curation Rewards table. Say you had a 25k delegation that expired and were left with 5k HP. Your Curation rewards would be from 30k HP but at the time I run the stats, you only have 5k and so would look like a CR genius.

Once on the list though, you will always appear in the Engagement League if high enough :)