Contribution functions computed in 3D NLTE at different x-positions for the same three selected wavelengths of the 525.0 nm line as in Fig. 3: a) line core; b) line flank; c) continuum. The dotted contribution function is given for every tenth grid position corresponding to Δx ≈ 35 km, starting at 10 km from the plane of symmetry of the flux sheet. The five contribution functions corresponding to the same x-positions as the profiles shown in Fig. 4 are highlighted (solid lines) and indicated by their x-position. Note the very different shapes and positions of the individual curves.