Hello! I've written up a tutorial about the theory behind the oto.ini--how it works and what it's trying to do. Unfortunately, there are too many pictures, so I can't post it directly here and will instead have to send you over to the UTAU wiki. This tutorial assumes some foreknowledge of how otos work, so it's not advised for beginners, but it might be understandable to them too? It's mostly for people who kind of understand otos but would like to improve their otoing skills.
Go here to see the tutorial!