log τ_Ross of the line-forming layers of the lines preselected in Sect. 3.3 as functions of the EP, the X index at 3850 K, the model depth d_OnlyOne , the model EW, and the reduced model EW. Top and bottom panels show the results with employed line lists of VALD3 and MB99, respectively. The vertical error bar represents the range of Rosseland-mean optical depth where the contribution function for the line is larger than the half of the maximum value at log τ_Ross. Horizontal black dashed line at log τ_Ross = −3.0 indicates the final criteria of our line selection.