  The companions of evaporating binary pulsars (black widows and related
systems) show optical emission suggesting strong heating. In a number of cases
large observed temperatures and asymmetries are inconsistent with direct
radiative heating for the observed pulsar spindown power and expected distance.
Here we describe a heating model in which the pulsar wind sets up an
intrabinary shock (IBS) against the companion wind and magnetic field, and a
portion of the shock particles duct along this field to the companion magnetic
poles. We show that a variety of heating patterns, and improved fits to the
observed light curves, can be obtained at expected pulsar distances and
luminosities, at the expense of a handful of model parameters. We test this
`IBS-B' model against three well observed binaries and comment on the
implications for system masses.
