I don't really have a suggestion - this is just a heads-up. Although, many websites can tell what platform you're using. Could the image just be anchored if you're on a mobile device? (Also, no pun intended.)

I can't really view the pop-up images at all on my Kindle.

Oho, yes, I see the problem as I start writing this comment on my phone!

Multiverse really needs a full mobile view. But this is particularly unusable on mobile so I'll try to fix it up ASAP.

(Link: I think this is to do with the newly deployed position:fixed on card pages, not card popup previews, though they're definitely another area that could work better on mobile too.)