Top panels: colour–stellar mass diagram that compares the spectroscopic targets (coloured points) with photometrically selected cluster galaxy candidates (black+green+red). Our method of subtracting fore- and background interlopers relies on the spectroscopic subset being a representative subset. Left panel: quiescent galaxies, for which this criterion is not fully met at low masses. Right panel: star-forming galaxies, for which this assumption is valid. Lower panels: spectroscopic targets shown as a function of cluster-centric distance and stellar mass. The ellipse shows the relative weight we give to either parameter when defining the five closest sources in this plane (which are used to estimate membership for the black points). Dashed region defines the population studied in this work.