  It has recently been proposed that radio emission from magnetars can be
evaluated using a "fundamental plane" in parameter space between pulsar voltage
gap and ratio of X-ray luminosity Lx to rotational energy loss rate Edot. In
particular, radio emission from magnetars will occur if Lx/Edot<1 and the
voltage gap is large, and there is no radio emission if Lx/Edot>1. Here we
clarify several issues regarding this fundamental plane, including
demonstrating that the fundamental plane is not uniquely defined. We also show
that, if magnetars and all other pulsars are different manifestations of a
unified picture of neutron stars, then pulsar radio activity (inactivity)
appears to be determined by the ratio Lx/Edot<1 (Lx/Edot>1), although
observational bias and uncertainty in the ratio for some sources may still
invalidate this conclusion. Finally, we comment on the use of other pulsar
parameters that are constructed from the three observables: spin period P,
period derivative Pdot, and Lx.
