Nested Platform Category not displaying icon in Sidebar

[VodkaParalyzer]

While importing my MAME roms, it gives you the option to create Playlists based on the Publisher

I like these, but not nestled amongts the other Auto Generated Playlists, so I added a Platform Category called, Arcade Publishers

I then moved each of the Arcade Publisher Playlists to appear under this

Now, I want to assign an icon in the Sidebar for my Arcade Publishers Playlist, but haven't been able to do so

I've found how to override other image types, by adding images to the Playlist and setting the Image Type, but that doesn't cover the Sidebar icon, that I can tell

I've tried naming it after my Playlist name and placing it in the various folders, but still no luck

Hoping there's something simple that I'm overlooking

TIA!