The effect sprite is always spawned at the particle object position. If you know which coin the particle object is attached to (say with hierarchy or pin), you can accurately pick that coin.
My effect sprites are given a small random offset in the particle parameters itself. There's a chance that, through sheer randomness, they could end up 'closer' to a different coin than the one that they are spawning from.
Currently, I have the coin spawning a particle system and adding that system as a child. The system then spawns effect sprites. The root of the issue is that there's no way to actually make the connection between the particle system and its spawned effect sprites, unless there's some way Scripting could access that?