Example of EW variations for the He I λ 4471 line for model E2 and for the O III λ 5592 line for model E4. The EWs have been normalized to the highest value. Black: primary. Grey: secondary. Top: variations measured on individual spectra (EW_p,max,HeI = 0.17 Å, EW_p,max,OIII = 0.18 Å, EW_s,max,HeI = 0.34 Å, EW_s,max,OIII = 0.11 Å). Bottom: variations measured on combined spectra (EW_p,max,HeI = 0.17 Å, EW_p,max,OIII = 0.14 Å, EW_s,max,HeI = 0.10 Å, EW_s,max,OIII = 0.08 Å).