Well you can try using the minefield behavior to help lower the object amount, but you'd have to create/remove bones to add more locations of where the effect could be played.
...OR...
You can make the object have a large hitbox and make it use the projectile/armor FX so when it gets "hit" by a projectile it would play the SFX. I'm not totally sure if it is exactly where the object hit though.
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