Question Particle System with bigger size is rendered behind the sprite.

I have a 3d scene with a simple sprite in the middle.
If I place particles in front of the sprite - it renders in front. If behind - it renders behind. (Not using any sorting order by index, etc. Just by the distance to the camera)
But if I increase the size of the particle system, all of the particles start to render behind the sprite, although they are still physically in front of the sprite.
What I mean by size: increased lifetime or increased speed or bigger shape but not individual particles. Anything that makes the particle system take a bigger space. If the space the particle system is occupying is somewhat bigger than the actual sprite it starts to render the sprite in front, which is clearly something no one would want.

I am assuming it has something to do with a pivot that the particle system creates always at the middle of the shape? No idea...
Please help?

 

Thank you for your answer!
If definitely works for static particles with scale.z = 0. But for moving particle system, which leaves particles behind itself in world space (which was my aim, I should have specified in the beginning) there is still a 3d bound being created because it is a 3d scene nonetheless, and therefore if the bound is big enough, it will be kicked behind the sprite. Is there perhaps any workaround for this case?