Top panels: the 21 cm power spectrum as a function of z at k = 0.05, 0.1, and 0.5 Mpc⁻¹. We show the same models and cases as in Figure 1: CDM (solid), WDM-like (dotted), and large-scale (dashed), for Dark Ages, moderate coupling, and saturated coupling. Bottom panels: the difference “Diff” in Δ² due to clumping. Panels with coupling show ∣−Diff∣, and also show the k = 0.05 Mpc⁻¹ sensitivity for SKA AA^⋆ (solid gray line and the corresponding shaded area) and SKA AA4 (dotted–dashed gray line).