  The source of the tension between local SN Ia based Hubble constant
measurements and those from the CMB or BAO+BBN measurements is one of the most
interesting unknowns of modern cosmology. Sample variance forms a key component
of the error on the local measurements, and will dominate the error budget in
the future as more SNe Ia are observed. Many methods have been proposed to
estimate sample variance in many contexts, and we compared results from a
number of approximate methods to estimates from N-body simulations in a
previous paper, confirming that sample variance for the Pantheon SNe Ia sample
does not solve the Hubble tension. We now extend this analysis to include the
more accurate analytic method based on calculating correlations between the
radial peculiar velocities of SNe Ia, comparing this technique with results
from numerical simulations. We consider the dependence of these errors on the
linear power spectrum and how non-linear velocities contribute to the error.
Using this technique, and matching sample variance errors from more approximate
methods, we can define an effective volume for SNe Ia samples, finding that the
Pantheon sample is equivalent to a top-hat sphere of radius
$\sim220~h^{-1}$Mpc. We use this link between sample-variance errors to compute
$\Delta H_{0}$ for idealised surveys with particular angular distributions of
SNe Ia. For example, a half-sky survey at the Pantheon depth has the potential
to suppress the sample variance of $H_{0}$ to $\sim0.1$ km s$^{-1}$Mpc$^{-1}$,
a significant improvement compared with the current result. Finally, we
consider the strength of large-scale velocity power spectrum required to
explain the Hubble tension using sample variance, finding it requires an
extreme model well beyond that allowed by other observations.
