[GeoffR]

Your goal is impossible with the current Kobo firmware, because it ignores the "file-as" field in the creator and title metadata (which is where Calibre puts the author_sort and title_sort metadata) and instead uses its own algorithm to sort based on the creator and title.

Edit: You could add the series tags after the author name and sort by author instead, but I don't think there is any way to do without the tags altogether. Back in version 2.3.2 the firmware would sort by series, but sadly that feature was removed from later firmware, and version 2.3.2 is too old to use on the Aura HD.