It took me longer than I thought to get back to my computer, thanks for the suggestions @barbarachicgeek @WPyogi @leejosepho !
I am working in a child theme for all my mods.
I just realized in the <h1>area wasn't the right place to take care of the linking - there is a <a href ... below it,
Looking here: "Common request from WP.com customers, make the header image a clickable link to home." - a change was made - http://core.trac.wordpress.org/attachment/ticket/22004/22004.diff.
I guess I'm not sure exactly where to define home_url or whether the php can be modified right there (& I'm not great with php just yet, so not sure what part of that should be changed)