I have a similar issue. I have a background sprite and an ammo sprite. Both the are in the same atlas. I want to add a shuriken particle system in between them (to make the ammo look like it is glowing). So the order would be, from back to front:
Background | Particle System | Ammo
The problem is, since the background and ammo are both drawn on the same draw call (because they are in the same atlas), when I mess with the Z of the particle system, it is always either behind or in front of both, but never in between.
Any idea how I could solve this problem without putting the background and ammo sprites in different atlases?
Thanks!