Why does my particles look different from a distance on iOS?

I've got a particle system that is supposed to look like this:

On the iOS player setting, this is what it looks like when your camera is right up close to the particle.

However when you zoom out and view it from a bit more distance it looks like this instead:

This problem does not come up when the player setting is set to desktop - only on iOS. What's going on and how can I fix it?