My response to the resolution note:

Thank you for examining this problem. To quickly explain my use case: I was making a dynamic decal system where each decal is placed at precise position determined by whatever caused the decal to spawn. System assumes each decal can have different parameters such as lifetime, color, position, size etc. If maximum amount of decals is reached then oldest decal is replaced by newly emitted one.

I decided to go with ParticleSystem because it handles a lot of things for me already such as z-sorting (even if multiple particles overlap on the same plane), batched mesh creation with customized attributes, fading, ring buffer and a lot more. From experience I know that often recreating such systems in managed code can lead to worse performance than Unity's internal systems so I tried to utilize ParticleSystem functionality as much as possible.

I was afraid that because in my case a lot of particles can be spawned at quick succession invoking .SetParticles over and over will create unnecessary overhead and decided to limit usage of that method to only removal of particles, which doesn't need to happen real-time.

The reason I wanted to remove particles in the first place is because after particles reach their lifetime they will not remove themselves from system because of ring buffer mode. That might be by design, however that is also causing ParticleSystem's culling not to properly cull the particles, because technically they still exist and they influence the bounding box, which now might be a lot bigger than it could be.

The other problem I had was that I needed to know the last index of the particle that was just emitted because I was using SetCustomParticleData to set additional parameters per particle after emission. I was also keeping my own array of data per particle that needed to exactly reflect ParticleSystem's array.

Knowing the issues beforehand I might've considered different solution (no ring buffer and manual control for example) however I ultimately found a workaround for the last index problem by studying when and why a particular index is being replaced and with some bookkeeping I was able to create a method that predicts last index in all cases, even after removing particles via SetParticles.

I will email another example project that will show how I did that in case it's at all helpful.