M_HI − M_⋆ best-fitting scaling relations to the stacking results from Bianchetti et al. (2025). Top: Linear fit to the data. Bottom: Polynomial fit. The data points are shown as blue squares (combined stacking), green diamonds (MIGHTEE stacking), and green circles (CHILES stacking), and the best-fit models as solid blue (combined stacking), dashed orange (MIGHTEE stacking), and dotted-dashed green lines (CHILES stacking).