Emergence of vortices in our simulations as a function of the gap depth. When no vortex was observed, we report both the observed gap depth at the end of our simulations, as well as the predicted one from Kanagawa et al. (2018), with a green circle (filled and unfilled, respectively). A red ⊗ symbolises those simulations where a vortex appeared, in which case only the predicted value from Kanagawa et al. (2018) is plotted. A dashed vertical line marks the approximate location of the transition between no vortex and vortex.