Observed and predicted cumulative PN numbers, as a function of radial distance from the center of NGC 3311. The green line shows the cumulative number of PNs associated with the central ICL halo of NGC 3311, based on their velocities. The black line shows the cumulative number of all PNs, without velocity selection. The red curve shows the predicted cumulative number of PNs computed using the luminosity-specific parameter α estimated as explained in the text, the MSIS observational set-up, and the integrated bolometric luminosity in increasing circular apertures centered on NGC 3311.