Relative difference between the input and measured parameters, flux density, effective radius, axis ratio, and Sérsic index (from left to right) obtained from Spergel fits to the uυ-plane (top panels) and Sérsic fits in the image plane using galfit (bottom panels) in our simulations plotted as a function of light concentration (i.e., Sérsic index) for various S_tot/σ_b and source sizes. Sources with a size of R_é/θ_b = 0.2 and 0.7 are marked by a diamond and a triangle, respectively, while the inset panel’s color bar shows the different input flux densities. The error bars denote the interquartile range of the distribution divided by the square root of the number of simulations.