The thing is, I have an action I run on each episode to format the tags already, so I don't have a list of files that feature the smaller art since I process each episode weekly and they're all up to date.
I should probably also mention the cover art changes per episode, which I'd forgotten to add to the OP. Because of this just wondered if there's a way to auto remove cover art based on dimensions at all since it's an extra step currently.
Alternatively if there was an option to change the drag-and-drop behavior of cover art so that dropping an image replaced the 'Front' cover instead of adding it as another image that would also save a step. Maybe as a modifier+mouse drop like Alt+Drop to replace whatever the particular visible art is, whether front/back/etc, might be one thing to consider (unless I've missed an existing option).