[Mg/Fe] vs. [Fe/H] for the UFDs with luminosities lower than 10⁴ L_⊙, for the models (in blue) and the observations (in gray). Contours, in black for the models and in red for the observations, represent the regions encompassing 30, 60, and 90% of the stars. The data contain a total of 49 stars from Bootes II (Ji et al. 2016d; Koch et al. 2009; François et al. 2016), Canes Venatici II (François et al. 2016; Vargas et al. 2013), Grus I (Ji et al. 2019), Horologium (Nagasawa et al. 2018), Leo IV (Simon et al. 2010; François et al. 2016), Reticulum II (Ji et al. 2016c,a; Roederer et al. 2016; Ji & Frebel 2018), Segue I (Norris et al. 2010a; Vargas et al. 2013; Frebel et al. 2014), Segue II (Kirby et al. 2013), Triangulum II (Venn et al. 2017; Kirby et al. 2017; Ji et al. 2019), Tucana II (Ji et al. 2016b; Chiti et al. 2018), Tucana III (Hansen et al. 2017), and Ursa Major II (Frebel et al. 2010; Vargas et al. 2013).