theducks beat me to it - it just seems a very strange thing to do, because as you say yourself calibre isn't going to sort your books to show them in that order, nor will they appear in order when you save to disk/send to device, so the question that comes to mind is... why???
I'm also in the same camp as theducks - I add a "Short" tag to books that are short stories, and if they are in a series like you have above then they get the fractional numbers. Then on my Kindle where I don't see the tags I have the fractional numbers to look at, plus the dotted line which tells me the length. Trying to put .SS in the series name just breaks all of that as well as being redundant.
So I'm afraid I don't see the plugin being changed to cater for this scenario.
