Marginalised posteriors from a subset of our inferences. From left to right, we show results for ${\overline{T}}_{21}$, ${\overline{T}}_{\mathrm{radio}}$, cumulative optical depth τ_rei(z), residual ($T_{\mathrm{sky}}-{\overline{T}}_{21}-T_{\mathrm{FG}}-T_{\mathrm{cal}}$), respectively. Each row corresponds to a different model, with the general trend of increasing systematics prior volume with decreasing row. The number of FG terms N_FG is indicated in the y-axis in the ${\overline{T}}_{21}$ sub-panels. Black solid lines and blue shaded contours show mean and 95% C.I. regions, respectively. In the ${\overline{T}}_{21}$ sub-panels, the green contours indicate the 95% C.I. assuming no radio background excess (i.e., setting f_R,III = 0 and only using the Planck likelihood), while the gray contours indicate the 95% C.I. using only ARCADE2 + Planck likelihoods (i.e., no EDGES). The green bar in the τ_rei(z) sub-panels denotes the 95% C.I. from Planck (Qin et al. 2020b) (see Eq. (31)). In the residual sub-panels, the ±2σ extent of the inferred Gaussian error σ_T is demarcated in gray.