I always char on a separate grill at around 450 degrees for 3-4 minutes on each side of a spatchcocked chicken. It's enough to blacken it nicely, and then I transfer over to the RT700.
How do you know they weren't done? Did you probe the ribs or do a visual test? I usually smoke baby backs at 225, and they have always taken around 5.5 hours. When probed, they will be 205-210. Let us know how you tested this.