Fraction of all satellite dwarf galaxies at z = 0 that were a satellite in another host halo any time prior to (left) or at the time of (right) falling into the MW/M31 halo, as a function of their current distance to the host, d, or as scaled to the host's virial radius, R_vir. Curves show the average over the paired MW/M31 halos in bins of satellite M_star, and error bars show 68% uncertainty in this fraction for a beta distribution (the halo-to-halo scatter is similar to Figure 4). For both group-preprocessing metrics, and across all masses, satellites closer to the host are more likely to have been preprocessed.