Outline of the test setup to determine the reliability of our model fit for each source. First, we generate a simple model image (left panel) consisting of a point source and an elongated Gaussian of arbitrary axis ratio and position angle. Since the intensity of the point source is largely model independent and well constrained by the observations, its visibility can be set to the actual value of the respective source. Next, this image is Fourier transformed (center left). From these model visibilities we take the values that correspond to the actually observed (u,v) coverage for the specific source (center right panel). After adding appropriate noise, we fit the mock data set with our three-parameter fit (minor axis FWHM θ_m, position angle PA, and axis ratio ϵ) and compare the result with the known input parameters. This procedure is repeated for different axis ratios and position angles and for the specific (u,v) coverage of each source.