Thank you davidfor, as always!
So, I tried:
Note I'm using latest calibre, latest plug-ins and Aura HD with 2.8.1
I used
{authors} - {#read} - {#words}
because all my authors are usernames (for fanfics) except a few and there's one in the pic, and I've tweaked author_sort to be the same as author because I like FN LN
I've created a new shelf with a few new books for the device, here's a picture showing what happens when i sort by author on that shelf.
So, it looks like it's sorting with the word number (weirdly, because a huge fic there was placed because its word count started by 2 only, same after a 54k book there's a 6k one).
IF i don't have a wc or a read value (ie: the books that were already on the device before I did this and only have the author in the author space) the books are sorted at the end of the list.
Those with - - because there's the undefined value for the read column don't mess up the order that goes with the first number of the word count.
And I don't really mind that there's Yes and - - , I know what that means and it's ok
I'm actually fine with this result, I don't sort much by author, I usually just search for one or just browse my shelves with date added or recently read order.
But I really like to immediately see if I've read the book or not and the word count [I used to put it on the cover of the fic if it was without a proper one but I had to go to the details to read it anyway, this saves me many clicks].
I'll soon delete and re-add all my other books so if you want more testing of other things... just tell me