I am unexperienced in VFX, and particle emitters, however I may have ONE idea that I would personally use:
Instead of one massive part above the map, try using multiple parts and changing the drag and lifetime values of the particle emitters in parts above the buildings.
Generally, I can’t help but that would be an idea that I personally have. I am interested to dive into a system like this, so if I can get information on that I will revisit this thread.