Relationship between extinction and the position of the dust clumps along the line of sight. The upper panel displays how the observed extinction A_observed relates to the fraction f of light in front of the dust for different values of real extinction A_real. The lower panels display how the fraction f relates to the line of sight distance z with respect to the center for different projected distances Y to the center along the minor axis. We detect a near/far side asymmetry, which strengthens the effect of absence of observed extinction on the far side. We rely on the modeling of Tempel et al. (2011).