How much useful Lingering Illusion as decoy?

I'm trying to understand, how much Lingering Illusion is useful as decoy and distraction for enemies and not for power charges? How effective it is from decoy/distraction perspective? Because so far what I've seen - even if illusion appears before the pack, entire pack still goes after my character and rarely single monster from entire pack decides to pay attention to the illusion.

Maybe I'm using it incorrectly?