Ah, I see where I messed up now.
I had previously tried
Generate Calibre Cover: Yes, Always which did everything I wanted when it came to the XenForo works I had, but it also replaced the author-provided covers for Scribble Hub as I had GC set to generate Scribble Hub covers in the GUI. I had forgotten that I can unset it from the GUI and add it in the ini file as
${cover_image} => ((first)|(default)|(^$)) => ScribbleHub which would keep the author-provided covers but use GC for the default ones.
Thank you for being so helpful and I'm sorry for wasting your time with something this trivial.
