Left panel: [Mg/Fe] distribution predicted by our best-fit model computed at 8 kpc (green histogram) compared with the APOGEE data in stars with Galactocentric distances between 6 and 10 kpc. Black and green vertical dashed lines indicate the median values of the data and model, respectively. Distributions are normalised to the corresponding maximum number of stars, N_max. Right panel: same as the left panel, but computed for a limited metallicity range, −0.2 dex ≤ [Fe/H] ≤ 0 dex, as highlighted by the green shaded area in the inset.