Phase difference φ_Q1−φ_M1 between the fundamenals of the fits of the measurements of ⟨ B_q ⟩ and ⟨ B ⟩ by functions of the forms given in Eqs. (16) and (17), against stellar rotation period. The meaning of the symbols is the same as in Fig. 13. Shaded zones correspond to forbidden regions where points are not expected to be found (see text for details). Two stars that depart from this expected behaviour (one of them marginally) are identified.