The nine Enneagram personality types by themselves don't adequately describe the variations in personality. Additional concepts have been added to the system over the years in an attempt to do this (e.g., wings, instincts, Tritype). This book describes these concepts and the many variations of type that result from applying them to the nine types.
This book, the 2nd planned book in the Enneagram User Guide series, is currently being written. Expected publication is spring 2018.