v1 line flux (top) and vibrational ratio of CO (bottom) versus the inferred radius of emission for observational data and DALI model results. Lines connect the dots in order of inner model radius. Labels indicate the gas-to-dust ratio for the thermo-chemical models, the LTE model also has a gas-to-dust ratio of 100. The model with the largest cavity has the largest CO radius. The dust surface density is kept constant for models of different gas-to-dust ratios. Due to missing data, not every source with a vibrational ratio in the lower panel also has a line flux in the upper panel. Clearly none of these models reproduce the trends in the data.