Left panel: Peak-to-peak RV (Δv) as a function of stellar radius for the BAF supergiants and the B3 supergiants of Britavskiy et al. (2025). Radii were determined using effective temperatures and luminosities from Table B.3. The sizes of the symbols in both panels are determined by Δv/σ_Δv. Black circles mark stars of the cohort of variable late-B-type bright giants. Right panel: HRD for BAF supergiant sample using stellar parameters listed in Table B.3; symbols have the same meaning as in the left panel. We note that the sources with largest Δv/σ_Δv tend to be the most luminous and hottest stars.