Redshifts and velocity dispersion distributions used for simulations. Top panel: redshift distributions of the lenses (red) and sources (blue) in the simulated training set. Bottom panel: lens velocity-dispersion distribution, predicted from the K-nearest neighbor algorithm (red) and shifted to match the criteria of pairing lenses and sources (orange), as described in Sect. 3.2. We note that the actual lens velocity dispersions used in the simulations are shifted to higher values, so that lensing features can be seen even at the DES resolution.