Redshift distribution of sky-localization uncertainty (given as 90% credible region) for three detector configurations: ET, ET+CE, and ET+2CE. The absolute numbers refer to the fiducial BNS population sample and detections within a redshift of 1.5 per year of observation assuming a duty cycle of 0.85 (see text). The panels show the detections and the corresponding sky-localizations as a function of the redshift 15, 5, and 1 min before the merger and at the merger time. The blue histogram (“All”) shows all the detected sources.