M(a) relation implied by the RP0 and Ep models. The thick black curves correspond to the geodesic case, i.e. these are the same curves as those shown in Fig. 2. The grey shaded region indicates the case when β >  0. The thick red curves correspond to β = β_cusp and the dotted red curve to β = β_∞. The dashed red lines correspond to β_eff = β/β_∞ = 0.7 and β_eff = β/β_∞ = 0.3. The black arrow labelled Δa indicates the shift of the upper limit on the spin of microquasars implied by the RP0 model considering the non-geodesic flow (from a ∼ 0.55 to a ∼ 0.83).