I personally use this
Code:
{author[0]}/{authors}/{series}/{series_index:0>2s}. {title}
It puts the books by
A\Author\Series\01 Title
something I would recommend compared to what you have shown above as
this will sort the books by series number as well.
or you can use this
Code:
{author[0]}/{authors}/{series}/{series_index:re(^(\d)(\.|$),0\1\2)||. }. {title}
it will also sort your short stories properly if you have them in a series