Left panel: comparison of fsbeam of detector 143-5 (full line) to the retrieved model (dashed line). Right panel: comparison of Mars-based beam of detector 143-5 (full line) to the retrieved model (dashed line). The Mars-based beam shows extended modelled shoulders that are not present in fsbeam, but are present in the model beam. The inference is that the use of fsbeam introduces non-optical features in the beam.