We could do with having the mobile and platform (or quality) specific LOD settings exposed in UEFN, especially as we ship to all platforms. This is the same functionality that is available within Unreal Engine.
Currently in UEFN, within a Static Mesh asset, under LOD, you can customise the Screen Size for all platforms. There is the plus icon which reveals a drop down for specific platform overrides, but when you click any of the options, it does not add another Screen Size option for the platform clicked.
I do not know if it has intentionally been set up this way, or if it is bugged (hence the Bug Report and Feature Request tags). If you could please fix or enable this functionality for performance and visual reasons, it would be greatly appreciated!