Left panel: inner density slope of the dark matter halo of the simulated lenses, γ_DM, obtained by fitting a gNFW density profile to the projected surface mass density of a lens, as a function of the logarithm of the ratio between the stellar and dark matter halo mass. Middle panel: γ_DM as a function of the logarithm of the ratio between the stellar half-mass radius and the average half-mass radius of galaxies with the same stellar mass. The latter is given by Eq. (15). Right panel: γ_DM as a function of the gNFW concentration parameter, defined as the ratio between the virial radius and the scale radius obtained from the gNFW profile fit. The vertical dashed line marks the value of c₂₀₀ adopted for the NFW profile describing the initial (pre-contraction) density profile of the dark matter halo.