Top row: pairwise relationship between α₀, ν_char and γ (cf. Eq. (2)) best-fit parameters for our sample of OB stars. Bottom row: location of stars in the spectroscopic HR diagram as filled circles that are colour-coded by the best-fit parameters α₀ (left) and ν_char (right), and have a symbol size proportional to the fit parameter α₀. Evolutionary tracks (in units of M_⊙) from Burssens et al. (2020) are shown as solid grey lines and the dashed grey line represents the ZAMS. A typical spectroscopic error bar for our sample is shown in the top-left corner.