Metallicity effect on the LL intercept, α_M, as defined in Eq. (3). The left panel shows α_M as a function of the effective wavelength 1/λ for a pivot period of log P₀ = 0.7, while the right panel shows the comparison for Wesenheit magnitudes and for log P₀ = 1.0. Our predictions based on SYCLIST, letting the LL slope vary or be fixed to that of the LMC, and IS edges are shown in black, pink, and grey, respectively. Observational results from B22 and SH0ES (R22) are shown in green in the left and right panels, respectively. In the left panel, the vertical dotted lines show the location of all the photometric passbands considered and we label some of them to orient the reader.