Leftpanel (a and c): 1401c model contribution functions through the atmospheric height for lines involved in transitions 2780.6 Å (a) and 71 097 Å (c). Right panel (b and d): effective collision strength (ϒ_ij) data at the formation region temperatures that were used to compute the populations for 2780.6 Å (b) and 71 097 Å (d) transitions in models 1401b (purple dashed-dotted line) and 1401c (red dashed-double-dotted line). The ϒ_ij data provided by the DW method are greater than the SEA&VRM for all the transitions studied.