Left: Histogram of the distance to the phase centre for the primary (open histogram) and secondary (grey histogram) counterparts. Right: Distribution of the Band 7 (870 μm) peak fluxes of the 209 ALMA sources in the 152 quasar fields (black histogram). Primary counterparts, that is, those extracted at the phase centre (i.e. at the optical coordinates of the quasars), are shown in a shaded histogram.