If I have a layouts/_default/rss.xml, it can generate RSS for every home, section, and taxonomy. But if I configure an Atom media type and output with an “atom” base name, and define layouts/_default/atom.xml, no atom.xml file is generated anywhere. I have to name it layouts/_default/list.atom.xml, and then it will work for home, sections, and taxonomies. layouts/_default/atom.xml should work like layouts/_default/rss.xml.