Ratio between the square visibility in the continuum (average between 2.27 and 2.28 μm) and the square visibility in the CO (2−0) line vs. log(L/L_⊙) (top), log(g) (middle), and the effective temperature (bottom) for the sample of RSGs (Arroyo-Torres et al. 2013; Wittkowski et al. 2012; this work). The dotted black lines show the range of predictions by the best-fit PHOENIX model of these sources, and the dashed orange the range of predictions by the best-fit RHD simulation. Both lines are overlap. The dashed gray lines, in the top and middle, show linear fits.