3D isotropic 21-cm signal power spectrum for a realistic cosmological setting at z = 12.2 (see main text) plotted for different modelling methods and codes. In the left panel, the IGM has been heated with a fiducial amount of X-rays (f_X = 1); in the right panel, the IGM has been subject to adiabatic cooling and heating only (f_X = 0). The expected SKA thermal noise level for 1000 h of observation (see the main text for further details) has also been plotted to quantify how the Lyman-α modelling could bias parameter inference performed on SKA observations.