  We investigate the prospects for constraining the maximum scale of clumping
in composition that is consistent with observed Type Ia supernova flux spectra.
Synthetic spectra generated without purely spherical composition symmetry
indicate that gross asymmetries make prominent changes to absorption features.
Motivated by this, we consider the case of a single unblended line forming in
an atmosphere with perturbations of different scales and spatial distributions.
Perturbations of about 1% of the area of the photodisk simply weaken the
absorption feature by the same amount independent of the line of sight.
Conversely, perturbations of about 10% of the area of the photodisk introduce
variation in the absorption depth which does depend on the line of sight. Thus,
1% photodisk area perturbations may be consistent with observed profile
homogeneity but 10% photodisk area perturbations can not. Based on this, we
suggest that the absence of significant variation in the depths of Si II 6355
absorption features in normal Type Ia spectra near maximum light indicates that
any composition perturbations in these events are quite small. This also
constrains future three-dimensional explosion models to produce ejecta profiles
with only small scale inhomogeneities.
