PL relations for T2Ceps based on the reddening values from Schlafly & Finkbeiner (2011) and reddening vectors (R_λ) from Green et al. (2019). We show the BL Her- and W Vir-type stars adopted for the derivation of PL relations (filled circles and squares); stars with RUWE > 1.4 (open marks); stars manually rejected from the fit (red crosses; see Sect. 3 for an explanation); a first-overtone Type I Cepheid (yellow star); pW Vir-type stars (cyan diamonds), RV Tau-type stars (magenta triangles), the fit to Eq. (1) for BL Her and W Vir stars separately as well as combined (solid line), analogous fit to Eq. (3) (dashed line), and the ±3rms for BL Her and W Vir stars and the combined sample (shaded areas). The pivot logarithms of log P₀ = 0.3,  1.2,  0.7 were used to fit the BL Her, W Vir, and combined sample, respectively.