Prograde equal-mass fly-bys: the mean initial distances to the infalling galaxy’s centre, and , for particles on pro- and retrograde orbits after the interaction. Upper panel: all particles with apocentre distances above 30 kpc are taken into account. There is a clear trend that retrograde particles originate from further out. Lower panel: the mean initial distances and show a better distinction, the before mentioned trend is more pronounced when only considering particles with apocentres above 60 kpc. All models of Tables B.2 were included, except models 6deg180vel, 7deg180vel and 8deg180vel as there are no far retrograde particles found.