I'm trying to emit particles from a layer with Particular. Everything looks fine at first, but when I turn on motion preview, I see that Particular is emitting particles at all points, not just from my logo. I would expect particles to be emitted only from areas that have an alpha channel, and not from areas that are transparent. My suspicion is further confirmed when i turn on the auxilary system and emit particles from particles. How can I get Particular to emit particles ONLY from areas of my layer that are opaque?
screenshot:

project file:
4553_layeremitter.aep.zip