Evolution of the theoretical Rossby number for the 2.7 and 2.85 M_⊙ dedicated models (blue and magenta respectively). The full and dotted lines correspond to Rossby numbers computed with the turnover timescale taken, respectively, at half a pressure scale height above the base of the convective envelope and at its maximum value within the convective envelope. The rectangles correspond to the expected position of 31 Com and OU And, taking into account uncertainties in their effective temperatures.