Differential core formation efficiency (CFE) as function of ambient cloud column density expressed in A_V units (blue histogram with error bars), obtained by dividing the mass in the form of candidate prestellar cores in a given column density bin by the cloud mass observed in the same column density bin. The upper x-axis provides an approximate mass-per-unit-length scale, assuming the local background around each core is dominated by the contribution of a parent filament with a characteristic width W_fil = 0.1 pc (see end of Sect. 4.5). The vertical dashed line marks the fiducial threshold at 7. The horizontal dotted line marks the rough asymptotic value of ~15% for the CFE at A_V > 15.