Here is the explanation from dev:
https://www.spacetimestudios.com/sho...e-and-boss-dmg

Elite maps are all maps under "Elite" category including the raids and maus m4+.
The last I checked %Elite Damage didn't work on raid bosses, so I think it is limited to mob damage. %Boss Damage works on any boss - normal or elite.
This info is more than 6 months old because I was off, please test this and update the thread or may be a dev can confirm the same.