MCMC posterior distributions for the five parameters of our $L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime }}\left(M_h\right)$ model, obtained from the analysis described in Sect. 2.3 of the main text. The inner (outer) contours of each 2D distribution show the 39% (86%) or roughly 1σ (2σ) confidence regions. The grey triangle in the 2 D probability distribution between A and B shows a never-accessed region where A > B; the MCMC treats the two parameters as an interchangeable pair, with the smaller (larger) of the two always subjected to the prior for A (B). Dashed lines represent the loosely informative “UM” priors discussed in Sect. 2.3.