I changed the spell over from Fear vs Fort to Charm vs Fort. Fear is suppose to be for non-magical attacks and I think you'll find the new contest favors Bards slightly more than before.
On an semi-related note I looked at it, the debuff is fully powered each pulse so I'm don't believe any special consideration need be taken for diminishing returns.
-Raesh
"Ever notice that B.A.'s flavor text swells in direct proportion to how much one of our characters is getting screwed?" - Brian Van Hoose