What kind of sprite can I feed into a particle emitter in Harmony 12 prem.?

I have a pound £ sign shrinking in size over 10 frames between two key-frames. I made this outside of the basic particle system. I can see the control path and scrub the play head to watch the £ shrink. When copied, pasted, and used to source my sprite emitter in the particle system I lose the shrinking effect. On selecting the sprite the path is visible but does nothing. Are we limited to a sequence of drawings for our sprite?

Also, on frame 23 of the twinkle_particles example there is a path shown in green which is un-selectable. What does that do and why can’t I select it?

Thank you.

See the Sprite Selection section for info on how to control it:
http://docs.toonboom.com/help/harmony-12/premium/Content/_CORE/_Workflow/031a_Particles/122_H1_Sprite_Emitter.html?Highlight=sprite emitter

“Use Frame Number” may work for your situation.