How to place novella in series

[Imzadi]

I am asking because of this book:

https://www.goodreads.com/book/show/5...

It is a novella and the authors webpage placed it as book 5.

https://kerriganbyrne.com/books/the-g...

As the book was numbered as 1.5 on goodreads, I changed it, which was undone. Which numbering is correct? I know, that it's not a primary work,

[rivka, Former Moderator]

It's certainly not #5 on Goodreads, as it is a novella. Novellas in a series containing novels get decimals.

The question is only whether it falls between books 1 and 2 (and would be 1.5) or between books 4 and 5 (and would be 4.5).