From a learning perspective, it was good to dig a bit into 2D vs 3D audio and understand PlayClipAtPoint.
But to avoid being forced to use sound attenuation in this manner, it might be cleaner to just attach an audio source to the death particle prefab itself and have it play on awake when the prefab is spawned. It would keep all audio playing in 2D, and the code/editor a little neater.