syncing non Store purchased epub book across devices

I purchased a book in epub format directly from the author and not through the Apple Store. I was able to get this book on my iPad via iTunes. On all of my iDevices I have "Sync Collections" turned on, and created a new collection to hold this and similar books.

The collection itself immediately synced across the devices, but the book itself did not.

Is it only store-purchased books that sync across devices via iCloud? Is there a way to sync titles purchased outside the Apple system across devices, or is one limited with non-Apple purchases to use iTunes and a wire (or wifi) to get titles to separate devices?