Surface brightness reconstruction for lensed source S3 at redshift z = 3.4280 from two different extended image models. We show the nearby group members included in the light modeling, while other objects within the gray regions are masked out. From top to bottom: Observed HST F160W images, the best-fit models, the normalized residuals in the range −9.5σ to 5σ, and the reconstructed source-plane morphology. Left column: Reconstruction from model Esr2-MP (L), which shows excellent residuals for the rightmost arc but significant overfitting of the light emission from the compact counterimage on the left. Right column: Same but for model Esr2-MP_test (L) based on a new mask that excludes the upper faint, diffuse region of the arc. This model improves the fit of the counterimage of S3.