Results of Plummer fits to Plummer-shaped synthetic filaments with a central column density contrast C⁰ = 1 and two distributions of D_flat inner diameters [flat in panel a; power law in panel b]. Two sets of D_flat measurements are provided depending on whether the power-law index p of the Plummer model profile was fixed to p = 2 [(1), yellow histogram] or left as a free parameter [(2), blue histogram]. The input distribution of D_flat values are shown by the black dashed histogram in both panels. In the left panel a, the input mock filaments had a fixed input p = 2 and a flat input distribution of D_flat between 0.03 pc and 0.34 pc. In the right panel b, the input mock filaments had a power-law distribution of D_flat diameters between 0.03 and 0.25 pc, similar to the distribution of FWHM widths in Fig. B.2B and B.4B, and a Gaussian distribution of p values witha mean of 2 and a standard deviation of 0.3. The power-law slopes of the measured distributions of D_flat diameters (shown as yellow and blue straight lines for the D_flat(1) and D_flat(2) estimates, respectively) are only ~ 30% shallower than the slope of the input distribution (black straight line).