Simulations of the p_mas vs. N relations in POL-2 observations. The calculations assumed a regular field (no geometrical depolarisation), an intrinsic polarisation fraction of p = 1%, and intensities proportional to the column density. The initial S/N of the total intensity at N(H₂) = 10²² cm⁻² at the full FWHM = 15′′ resolution is either 40 (open circles) or 200 (solid circles). The black, blue, and red colours correspond to the convolution to a resolution of 20′′, 40′′, and 80′′, respectively. For comparison, the dashed lines show the least squares fits from Fig. C.2.