  Switching diagrams of nanoscale ferromagnets driven by a spin-transfer torque
are studied in the macrospin approximation. We consider a disk-shaped free
layer with in-plane easy axis and external magnetic field directed in-plane at
90 degrees to that axis. It is shown that this configuration is sensitive to
the angular dependence of the spin-transfer efficiency factor and can be used
to experimentally distinguish between different forms of $g(\theta)$, in
particular between the original Slonczewski form and the constant $g$
approximation. The difference in switching diagrams is especially pronounced at
large spin polarizations, with the Slonczewski case exhibiting an anomalous
region.
