Comparison of the recovered image-plane results with respect to the input model, for D|$_{\rm 2}$| (source = |$s_{\rm 1}$|⁠, |$P_\mathrm{ f}$| = 3 per cent, i = 90 deg; top) and D|$_{\rm 7}$| (source  = |$s_{\rm 2}$|⁠, |$P_\mathrm{ f}$| = 12 per cent, i = 45 deg; bottom) at 2 and 3 GHz, as an example (note that we simultaneously model all channels). The rows contain Stokes |${\boldsymbol {I}}$|⁠, |${\boldsymbol {Q}}$|⁠, and |${\boldsymbol {U}}$| from top to bottom. We do not show Stokes |${\boldsymbol {V}}$|⁠, but find results consistent with zero surface brightness, in agreement with our input model. For clarity, we mask the colour maps to include only the region of the highest SNR, where the input surface brightness Stokes |${\boldsymbol {I}}$| is at least 20 per cent of the peak. The residual RMS values are computed within the same mask.