Impact of using a filtered ionizing continuum instead of a simple powerlaw on the observed values of Lyα/HeII, Lyα/Hβ and η_Lyα. In order that the curves be aligned, the models are plotted as a function of log U_* where U_* = U/F_esc. In the upper panel, the U_*-sequences using a filtered ionizing continuum are labelled with their respective value of F_esc. U_*-sequence loci which use our default powerlaw of α = −1.5 are labelled “1.0” because the input SED is unfiltered. The dot-dashed curve (on the right of the upper panel) shows the locus of our sequence in U_* that uses F_esc = 0.28, Z/Z_⊙ = 0.01, α = −1.5 and the “front view”, to illustrate the combined effect of low U_*, low gas metallicity, a heavily filtered ionizing continuum, and a “back-mirror”. For each combination of U_* and Z/Z_⊙, a lower F_esc results in a lower Lyα/HeII.