Uncertainty on the uv-domain (upper panel) and image-domain (lower panel) stacked size measurements of 100 simulated galaxies as a function of their intrinsic flux densities and sizes. Lines and symbols are the same as in Fig. A.1. Our stacking analysis allows accurate mean size measurements (i.e., ) for galaxy populations that are otherwise individually undetected, i.e., with intrinsic flux densities lower than the vertical dashed pink line.