Average scaled density of the synthetic models from Fig. 8 in the Kepler/TESS bandpass (400–900 nm), shown as a function of ΔIW and Ψ_VMF (coloured lines and dots). The colour corresponds to ξ. The simulations are compared to the inferred scaled densities for 55 Cancri e and TOI-1408 c, which are shown as grey bands; their width denotes the 1σ limit. The dashed black line indicates the scaled density of an atmosphere-free (airless) planet, i.e. R_p,MAI (Sect. 2.1.1).