Mass–period distribution of observed MS–BD binary systems used in this study. The colour scale indicates the mass of the host MS star. The top and right histograms, with kernel density estimates (KDEs), show the distributions of the orbital period and BD mass, respectively. The dashed grey lines indicate the BD mass range, while the dashed green line marks the BD desert transition mass of 42.5 M_Jup from Ma & Ge (2014).