Distribution of [α/Fe] for GALAH stars in the vertical segment of the HPMS (−1.0 < [Fe/H] < −0.5). The top and bottom panels show [α/Fe] as a function of L_Z for stars in the inner (r_ap < 10 kpc) and outer (r_ap > 12 kpc) regions, respectively. High-α stars are shown in blue and low-α stars in red. The high-α population dominates the inner region and exhibits a relatively constant [α/Fe] over a wide range of L_Z. In contrast, the low-α stars display a bimodal L_Z distribution: the low-L_Z stars are primarily associated with GSE, while the high-L_Z stars may trace the high-Z_max tail of the thin-disc population.