Left panel: evolution of the surface density calculated within the half-mass radius, Σ_∗,<50%, as a function of the half-mass radius compared to observation of the present-day MW GCs (gray dots) and high-redshift observations of proto-GCs (black symbols). Orange crosses and blue dots indicate the initial and 12 Gyr snapshots of the simulations. Right panel: normalized version of the left panel where each simulation is color coded according to its initial tidal filling factor. This plot shows that in this parameter space, GCs follow a similar track: after 12 Gyr of evolution, the surface density decreases by a factor of ≈1–6 × 10⁻², and the half-mass radius increases by a factor of ≈3–5.