I agree. "Between Two Fires" does a pretty good job of identifying where Native Americans participated in small or large units. It does a very poor job of characterizing the troops in the Indian Territory where you have several thousand Native American serving on both sides and higher per captita losses than any State. The best book on the military events in Indian Territory is Whit Edward's "The Prairie Was On Fire: Eyewitness Accounts of the Civil War in the Indian Territory". For those interested in the broader topic, I would recommend Annie Abel's "American Indian as a Participant in the Civil War" (which I believe the full text is available online).