What's the problem you are having?
Kobo devices do not use the author sort, only the author. It assumes any author is "LN FN" but doesn't handle two word surnames ("von Soandso"). "LN, FN" will work when sorting in the book list, but, Kobo uses the comma as the separator for multiple authors. The author collections are built based on the commas. So, "LN, FN" will produce collections for both "LN" and "FN".
And for the record, the plugboard I use for authors is:
Code:
{authors:'re(re($, '(.*) & ', '\1 and '), ' & ', ', ')'}