Measurement of pEW of He I IR as function of L_X (left panel) and of L_X∕L_bol (right panel). Symbols represent the pEW(He IR) of the valid sample with known X-ray fluxes, and colours decode spectral sub-type as in the legend in the left panel. In both panels, dashed lines with colours according to sub-type indicate hypothesise lower and upper envelopes where recognisable, while for the other spectral sub-types only lower envelopes are indicated.