3D isotropic power spectra of the 21-cm signal at z = 16.5 for three different models (see the main text for further details) plotted for two different ways of modelling the Lyman-α coupling (both without the contribution of gas velocities) and compared to the expected thermal noise of observations on the NenuFAR and SKA radio interferometers. The dotted black line shows the contribution from sample variance in the case of the exotic signal.