Adding Impact theme banners?

Greetings!

In the past – 2007-now, say — whenever I wanted to create a new theme using Impact, I would note the new blog # in my Dashboard, name my new banner that #, upload it to public_html > headers, and I’d be off to the races. No problems.

Headers-folder screen capture: https://composing.org/help_files/ftp_headers.jpg

Since 3.1, however (and I’m speculating on that connection — I’m an amateur) — that doesn’t work anymore. Blogs do not come numbered, and when I counted manually, adding a new banner based on that estimation, it did not work.

Dashboard screen capture: https://composing.org/help_files/dashboard.jpg

Make sense?

Does anyone know how to add a banner for Impact?

Thanks very much, in advance.

Best,

Michael