V_ϕ/σ_z ratio (azimuthal velocity to vertical velocity dispersion) for the most prograde Gaussian component in each metallicity bin (spaced evenly on a log scale) from our GMM runs in Section 6.3. The square size indicates the relative weight of the most prograde Gaussian in each metallicity bin. This ratio is a unitless quantity indicating the level of rotational support within a disc, essentially quantifying how dynamical cold it is at z=0. The dashed line at V_ϕ/σ_z=1 marks the boundary between pressure-supported (halo-like) vs rotation-dominated kinematics (disc-like).