So this was my original series cover...
It's just my Chapter One cover, but it's all I had for a while, so it was my Tapas cover image. And this was my thumbnail...

...which was just a cropped image from a page from chapter one that I liked.
Since then I've redone both to give it a proper series cover and a matching thumbnail...

Because I like consistency across my things! And I think this image makes for a better series cover than just using my chapter one cover.