Size of the penetration zone plotted as a function of convective Rossby number for the 17 SPB pulsators in Pedersen et al. (2021) whose best forward asteroseismic model is based on convective penetration (the symbol sizes scale linearly with the near-core rotation frequency, where the legends list the lowest and highest values). The full line represents the expected relationship according to the theory by Augustson & Mathis (2019), with a slope fixed at 3/10 and the intercept calibrated by the 17 observed stars. The dotted line represents the best linear fit, with its uncertainty region indicated in grey.