Upper panel: resulting histogram of significance values outside of the exclusion mask (0.8° centred on η Car) from the ring background analysis method as also used in H.E.S.S. Collaboration (2020) drawn together with a fitted Gaussian. The Gaussian strongly deviates from an ideal background description with width 1. For comparison the distribution of significances for the on-off method is shown as well. Lower panel: radial excess distribution from the ring background and the on-off background analysis centred at η Car compared with the point spread function (PSF) derived from simulations (scaled to match the on- off excess in the first bin). Additionally, the radial NSB profile is shown with arbitrary scaling.