Same as in Figure 5, but for the PT-BUBBLE (left panel) and PT-SOUND model (right panel). Figure 25 in Appendix C.3 shows the same plots but with the parameter a fixed by causality, a = 3. Figures 26 and 27 in Appendix C.3 show extended versions of the two plots that include the spectral shape parameters a, b, c and the SMBHB parameters A BHB and γ BHB.