Critical curves and caustics of the reference model P3ε for a source at z_src = 1.4255 (the mean redshift values of the sources). Left panel: tangential (cyan) and radial (magenta) critical lines on the image plane. The green circles show the observed positions of the multiple images belonging to the four families within Δz ≤ 0.0011. BKG1 is a background galaxy not multiply lensed by MACS 1206. Right panel: tangential (cyan) and radial (magenta) caustics on the source plane, and the reconstructed positions of the background sources.