Syncing imported books between 2 iOS devices

I've imported a bunch of books in ePub format into iTunes and synced them to my iPad Mini, all working great.

The problem i'm having is they aren't syncing over to my iPhone 4S, even though I have all the options ticked for syncing books and collections.

Am I wrong in believing that iBooks and iCloud should sync all books whether they are bought from Apple or not?

Thanks.