Left: examples of simulated RM images for the sources A401A, A401B, A2142, A2065, OPHIB. The simulated images have the same colour scale and resolution of the observed RM images. They have been obtained by simulating a RM power spectrum with a spectral index n = 11 / 3 and a minimum scale of the RM fluctuations Λ_min = 5 kpc. The maximum scale of the RM fluctuations is Λ_max = 205 kpc for A401A and A2142, Λ_max = 128 kpc for A401B, Λ_max = 15 kpc for OPHIB and A2065. Middle: structure functions of the simulated (grey) and observed (black points) RM images. Right: depolarization plots of the simulations (grey) and observations (black points). The depolarization is defined as DP(ν) = FPOL_ν / FPOL_{8465   MHz}.