Gray-scale figures of the contribution function along the cut at Y = 0.9 displayed in Fig. 5. Dark color corresponds to higher amplitudes. Contribution functions in each column are normalized to the highest value of the column. Heights with contribution function amplitudes equal to 10% of the highest contribution to the emerging intensity are marked with blue contours. Red solid lines represent effective formation heights. The various panels show results for 0.4 mm a), 1 mm b), 3.6 mm c), and 10 mm d). In all panels the y-axis scale is expanded. The dashed lines are the same as in Fig. 5.