Ratios of effective to mean opacity/optical depth for continuum absorption (left) and line absorption (middle, right), as functions of clump optical depth and for the parameters given in the panels and inter-clump density parameters f_ic = 0, 0.01, and 0.2 (where the f_ic = 0.2 curve is the upper one in each panel). Note that the clump velocity span is δν = δν_sm in the middle panel and δν = 5δν_sm in the right one. Red dashed lines show the effective opacity/optical depth laws indicated in the figure, blue triangles show results from the 3D-box experiments described in the text, and the black solid lines in the left panel show the analytic expression given in Appendix A.