χ² values for our grid of CS models for IRC +10 216. The contours denote 1σ, 2σ, and 3σ ranges, when constrained using only the spatial information from the CS J = 2-1 line (green) vs just the excitation information from the different J lines (blue). Also shown are the contours when using both the spatial and excitation information simultaneously (red) to constrain the RT models. The green, blue, and red stars mark the best-fit models estimated from the above three cases, respectively.