  The early lightcurves of Type Ia supernovae (SNe Ia) can be used to test
predictions about their progenitor systems. If the progenitor system consists
of a single white dwarf in a binary with a Roche-lobe-overflowing
non-degenerate stellar companion, then the SN ejecta should collide with that
companion soon after the explosion and get shock-heated, leaving an early UV
excess in the lightcurve. This excess would only be observable for events with
favorable viewing angles, $\sim$10\% of the time. We model the 2018 ZTF sample
of 127 SNe Ia using companion shocking models, and recover an observed early
excess rate of $12.0\pm3.6\%$, consistent both with several other rates
calculated throughout the literature, and with the expectation that SNe Ia
predominantly occur in single-degenerate systems. We observe early excesses
only in spectroscopically normal SNe Ia, in contradiction to the claim that
such excesses occur more frequently in overluminous SNe Ia. We also show that
the detection of early excesses can be methodology-dependent. We encourage the
observation of large samples of SNe Ia with high-cadence multiwavelength early
data in order to test the statistical predictions of SN Ia progenitor models,
and we also encourage the refinement of existing models.
