Posterior predictive distribution in half-light radius as a function of halo mass for galaxies with log M_* = 11.4. This is obtained by first drawing values of the hyper-parameters from the posterior probability distribution of our Sérsic model-based inference, then drawing values of R_e and M_h for 1000 galaxies, given the model specified by the hyper-parameters. Blue contours correspond to 68% and 95% enclosed probability. The cyan band shows the 68% credible region of the size-halo mass relation, obtained by fitting a power-law relation to the mock distribution of R_e and M_h at each draw of the hyper-parameters.