Inspired by @kmcquinn's ISM*-at-ST talk, the different parts of the CMD (HR diagram) are known to be better/worse understood (e.g., Hidalgo et al. 2011). This could be easily reflected in the megabeast fits by adding a model uncertainty term to the fitting. Or maybe this is a straight weight in the Bayesian formulation. Maybe @eteq can provide some advice here.