Histogram of the separations of the “high-confidence” sources (selected by colour) from their PN centres, along with, for comparison, a Rayleigh distribution with a similar mode in red, and a uniform density of background sources in grey. Lower panel: separation density ratio resulting from the derived mixture of Rayleigh distributions compared to that from the single Rayleigh distribution in the upper panel. In practice the mixture is re-weighted depending on the radius of the PN.