[DaveBlake]

Sorry, I somehow missed this when posted.

I don't want to have the album cover as artist thumb

Hum.... could be an unavoidable  side effect of Kodi trying to be backwards compatible in the way it picks up artist art for users with older folder and art layuouts while also handling disc level art. I will check, I agree it isn't the idea behaviour, but I suspect that if I change that I will break a more common use.