Thank you so much for all your effort, and my apologies for the slow reply! The theme layer fix worked like a charm... My header image is now the right size on mobile.

However, the layout layer doesn't seem to be having the desired effect. I copied in your code but nothing seems to have changed. I did see the piece you added, although I don't know why it's not working.

Thanks for the heads-up on the reading page title and subtitle. It's good to know that that's really only a core2 option. It's such a minor thing that it's definitely not worth going to a lot of trouble to import into core1.