Output versus true λ_thick estimation. The left figure shows the accuracy of estimating λ_thick when using GMBB-Sizes to fit the SED, in which it is derived using Eq. (7). The right figure shows the accuracy of estimating λ_thick when using GMBB-Lambda to fit the SED, in which it is a free parameter in the equation. The black dashed line is the identity line and the black squares show the median within each bin.