Histograms of the semi-axis ratios of thermal flare X-ray sources of various C–X-class flares observed with RHESSI (Warmuth & Mann 2013). The semi-axes were calculated from 2D elliptical Gaussian fits to RHESSI images calculated with four image reconstruction algorithms: clean (a), pixon (b), visibility forward fit (single elliptical Gaussian), and MEM-NJIT (d). 1D Gaussian fits to the CDFs of these distributions are shown in orange. The mean and standard deviation of the fits are shown in the legend of each panel.