Import at runtime from local file with spaces in the path

Unless I'm misunderstanding something or having a moment of stupidity - UnityWebRequestLoader breaks because the relative path is url encoded (so spaces become %20) by GetFileFromUri but then the File.Exists check in LoadStreamAsync fails because it doesn't unencode the spaces

I looked at using FileLoader instead but there's no documentation and it has wildly different behaviour when running in the editor (even in play mode) so I'm not sure if this is the right direction.

1. Should I be using UnityWebRequestLoader or FileLoader?
2. Is FileLoader's execution path differences in the editor intentional? Why is it trying to use the AssetDatabase?