Where do I add a second masthead image for mobile?

I’m using a Logo Image (so the entire image is clickable), but I’d like to replace the Masthead image on a Smartphone to a tighter crop. I see that I can add a second Secondary Masthead, if that’s where it goes, but it only has the same options as the Primary Masthead to turn on or off hi res. How do I configure an image for the mobile masthead only?

You’re not seeing these settings?

Is this a Pangolin page template?

Darn. I didn’t see Visibility Mobile. Sorry about that.