Constraints on the power-law slope α_z that governs the evolution of the volumetric binary black hole merger rate with redshift (top) and the peak redshift z_p beyond which the merger rate turns over (bottom), each as as function of primary mass. As in Figs. 3 and 5, the black lines show the 95% credible posterior bounds, the dashed cyan lines mark prior bounds, and the dotted magenta curves illustrate prior bounds after they were conditioned on the best-measured posteriors at m₁ = 35 M_⊙.