  Multiwavelength dust continuum and polarization observations arising from
self-scattering have been used to investigate grain sizes in young disks.
However, the polarization by self-scattering is low in face-on optically thick
disks and puts some of the size constraints from polarization on hold,
particularly for the younger and more massive disks. The 1.3 mm emission
detected toward the hot ($\gtrsim$400 K) Class 0 disk IRAS 16293-2422 B has
been attributed to self-scattering, predicting grain sizes between 200-2000
$\mu$m. We investigate the effects of grain size in the resultant flux and
polarization fractions from self-scattering using a hot and massive Class 0
disk model and compare with observations. We compared new and archival
high-resolution observations between 1.3 and 18 mm to a set of synthetic
models. We have developed a new public tool to automate this process called
Synthesizer. This is an easy-to-use program to generate synthetic observations
from numerical simulations. Optical depths are in the range of 130 to 2 from
1.3 to 18 mm, respectively. Predictions from significant grain growth
populations, including millimetric grains are comparable to the observations at
all wavelengths. The polarization fraction produced by self-scattering reaches
a maximum of $\sim$0.1% at 1.3 mm for a maximum grain size of 100 $\mu$m, being
an order of magnitude lower than that observed with ALMA. From the comparison
of Stokes I fluxes, we conclude that significant grain growth could be present
in the young Class 0 disk IRAS 16293 B, particularly in the inner hot region
($<10$ au, $T>$ 300 K) where refractory organics evaporate. The polarization
produced by self-scattering in our model is not high enough to explain the
observations at 1.3 and 7 mm, and effects like dichroic extinction or
polarization reversal of elongated aligned grains remain other possible but
untested scenarios.
