Well, I'm 6' and had this on a 5' tripod + head and they were still maybe 2 feet above. I think the wide angle this close makes them appear larger than they are, but then again, the middle figure is 9' tall.
Great image. I also like your cyanotype. I was in this area the end of September and had three non-photographers with me who didn't want to make the walk . . . I'll do it by myself next time. There is some rock art just outside of Moab which is also fairly tall. I've got to get to the Great Wall.