Distribution of the reduced chi-square χ_ν = 9² of the 58 individual fits and the population fit of 55 clusters. The red outlier with χ_ν² > 7 is SPT-CLJ0405-4916, which is characterized by a highly oscillating surface brightness distribution in its outermost region, while our background model, the pedestal, is a constant. For this reason, we excluded it from the population analysis.