Poloidal field component squared amplitude as a function of the Rossby number, Ro_f. At low Ro_f, the agreement between the simulations (purple line) and observation (dashed black line) is quantitatively good, with both showing a similar decreasing trend. At a higher Rossby number, Ro_f > 1 (yellow range), not covered by the observational database, an inverse trend is indicated by the simulations, and hence suggests a minimum in poloidal field strength near Ro_f ∼ 1, which could have interesting consequences for stellar spin-down via wind braking. An indicative trend proportional to is shown using a dotted grey line. We note the V shape that the two trends (purple and dotted lines) form, with the minimum being near Ro_f ∼ 1. The coloured symbols have the same meanings as in Fig. 3.