Location of the peak (i.e. flattest) spectral index within each disc, relative to the direction of the radio tail, in polar coordinates. The azimuthal axis shows θ_flat, and the radial axis shows r_flat (see the main text for details). The shaded region corresponds to 3.25″, the half width at half maximum of the beam. Angles greater than 90° correspond to points on the leading half (LH), and angles less than 90° correspond to points on the trailing half (TH). The peak spectral index is systematically found on the leading half (θ_flat > 0) of ram-pressure-stripped galaxies.