Source strong lensing bias in the case of a magnification-based lens definition (brown curves), compared to that of the fiducial analysis (blue curves). First panel: median source redshift. Second panel: median source magnitude. Third panel: median half-light radius in the magnitude bin 24.8 < m_s < 25.2. The dashed line indicates the median value of the population of sources detectable in the absence of lensing.