Environmental properties of MBH binaries and their host galaxies, for systems dominating the background (bck) and CW candidates (CW cand). From top to bottom, we show the chirp mass as a function of the stellar mass of the host galaxy and of the mass of the halo hosting the galaxy. Binaries hosted in central halos are shown as red squares; binaries hosted in subhalos are shown as orange crosses. An inner black marking highlights the high probability CW candidates.