question about Enfeeble on bosses

Hi all,

I've heard that curses are only like 30% effective on bosses?

Does that mean if I have a level 20/20 enfeeble that normally reduces the damage a NPC does by 34%, that for a boss it would only reduce their damage by 10%?

Or

... does it mean it is harder for the curse to work on the boss, but once they are cursed, they still have their damage reduced by 34%?

Yes, they work every time but their effect is reduced.

act bosses have 70% curse resistance
map bosses have 60% curse resistance
rogue exiles have 50% curse resistance