  We investigate the effect of the circumstellar medium density profile on the
X-ray emission from outer ejecta knots in the Cassiopeia A supernova remnant
using the 1 Ms Chandra observation. The spectra of a number of radial series of
ejecta knots at various positions around the remnant are analyzed using
techniques similar to those devised in previous papers. We can obtain a
reasonable match to our data for a circumstellar density profile proportional
to r^-2 as would arise from the steady dense wind of a red supergiant, but the
agreement is improved if we introduce a small (0.2-0.3 pc) central cavity
around the progenitor into our models. Such a profile might arise if the
progenitor emitted a fast tenuous stellar wind for a short period immediately
prior to explosion. We review other lines of evidence supporting this
conclusion. The spectra also indicate the widespread presence of Fe-enriched
plasma that was presumably formed by complete Si burning during the explosion,
possibly via alpha-rich freezeout. This component is typically associated with
hotter and more highly ionized gas than the bulk of the O- and Si-rich ejecta.
