HRD and mass distributions. Upper panel: HRD (T_eff−logL). The dashed grey and dotted lines mark the standard EHB band for a metallicity of −1.48 (Dorman et al. 1993). The horizontal dashed black line at log L=1.05 marks the luminosity limit separating bEHB stars from EHB stars (see Dawson et al. 2026). While the lowest luminosity stars HS2029+0301 and HS2240+0136 lie on this line, none of the other stars lie below it. Lower left: mass vs. T_eff. Helium-poor stars are marked in blue, extremely helium-rich sdOB and sdO stars in red, and iHe stars in black. Lower right: MC mass distribution as normalised KDEs for the three He subclasses. The shaded bands denote the uncertainty ranges.