Initial galactocentric radii (R₀) of the objects that are in the solar neighbourhood below 20 Myr (light blue) and above 20 Myr (dark blue), shown in normalised histograms with bins of 1 kpc. The dotted curve shows the initial radii of the total population, in a similar histogram. The distribution of the total population peaks slightly above the half-light radius, R_d = 2.6 kpc (Eq. (1)), because the spiral arms shift the initial positions to higher radii compared to the disc.