We show that the principle of minimum differentiation holds in two-round elections, for any number of candidates, regardless of the presence of entrants, or the distribution of voters' preferences.
Haan, M., & Volkerink, B. S. I. (2001). A Runoff System Restores the Principle of Minimum Differentiation. European Journal of Political Economy, 17(1), 157-162. https://doi.org/10.1016/S0176-2680(00)00033-1