Save single message with same file name pattern as saving multiple messages, no add-ons. about:config preference name?

When I save (Save as dialog) a single message in Thunderbird, I get a filename with just the subject. When I save multiple messages, the filenames are Subject-Sender-Date-time, which I prefer (although it'd be nice to set date-time first). Thunderbird, by itself, seems capable of the more specific file name format, yet there seems to be no setting to get this to apply to all save, single or multiple, much less one to change the order of the fields in the pattern. Is there a preference name in about:config that I should search for? Thanks!