  Traditional pulsar polarization sweep analysis starts from the point dipole
rotating vector model (RVM) approximation. If augmented by a measurement of the
sweep phase shift, one obtains an estimate of the emission altitude
(Blaskiewicz, Cordes, & Wasserman). However, a more realistic treatment of
field line sweepback and finite altitude effects shows that this estimate
breaks down at modest altitude ~ 0.1R_{LC}. Such radio emission altitudes turn
out to be relevant to the young energetic and millisecond pulsars that dominate
the \gamma-ray population. We quantify the breakdown height as a function of
viewing geometry and provide simple fitting formulae that allow observers to
correct RVM-based height estimates, preserving reasonable accuracy to R ~
0.3R_{LC}. We discuss briefly other observables that can check and improve
height estimates.
