Ratio of bound-only masses computed from an initial FOF group (by ROCKSTAR) and from all particles within ﹩{R}_{200{\rm{m}}}﹩ (by SPARTA), at z = 0 in TestSim100. The bound masses agree almost exactly for host halos (dark blue). For subhalos (light blue), there is a large fraction where the masses agree but also an extensive tail toward large values (the shaded areas show the 68% and 95% intervals for subhalos). The tail is caused by halos where ﹩{R}_{200{\rm{m}}}﹩ includes sufficient host particles to spuriously bind a lot of material. This case is more likely for ﹩{R}_{200{\rm{m}}}﹩ than for ﹩{R}_{500{\rm{c}}}﹩ because the latter relies on more strongly bound particles.