Same as Fig. C.1 but for β, the power-law index governing the decline in halo gas fraction for low-mass haloes. As can be seen from the bottom-right panel, increasing β makes the decline in gas fraction sharper, and this has a comparatively large effect on low-mass haloes as can be seen in the other panels on the right-hand side of the figure. High mass haloes are affected in the opposite sense because the gas fraction is forced to be 0.5 at 10¹⁴ h⁻¹ M_⊙. The effects on the power spectra can be seen in the left-hand panels, where the matter–gas spectrum can be seen to be most affected.