Set of 1000 power spectra randomly chosen from the 10⁵ simulated power spectra. Panels from top to bottom refer to z = 8.3, 9.1, and 10.1, respectively. These correspond to the scenario with no additional radio background other than the CMB (A_r = 0). The down arrow points refer to the recent LOFAR 1σ upper limit (Δ₂₁²(k, z)±Δ_21, err²(k, z)) from Mertens et al. (2025). As a reference, the dashed line corresponds to the power spectrum for a completely neutral IGM with no X-ray heating, and with T_S = T_K. The coloured power spectra are those with a value larger than Δ₂₁²(k, z)−Δ_21, err²(k, z) in at least one k-bin, i.e. they have a high probability of being ruled out, while those in grey have a low exclusion probability.