  Traditionally, the pair instability (PI) mass gap is located between 50\,and
130\,$M_{\odot}$, with stellar mass black holes (BHs) expected to "pile up"
towards the lower PI edge. However, this lower PI boundary is based on the
assumption that the star has already lost its hydrogen (H) envelope. With the
announcement of an "impossibly" heavy BH of 85\,$M_{\odot}$ as part of
GW\,190521 located inside the traditional PI gap, we realised that blue
supergiant (BSG) progenitors with small cores but large Hydrogen envelopes at
low metallicity ($Z$) could directly collapse to heavier BHs than had hitherto
been assumed. The question of whether a single star can produce such a heavy BH
is important, independent of gravitational wave events. Here, we systematically
investigate the masses of stars inside the traditional PI gap by way of a grid
of 336 detailed MESA stellar evolution models calculated across a wide
parameter space, varying stellar mass, overshooting, rotation, semi-convection,
and $Z$. We evolve low $Z$ stars in the range $10^{-3} < Z / Z_{\odot} < Z_{\rm
SMC}$, making no prior assumption regarding the mass of an envelope, but
instead employing a wind mass loss recipe to calculate it. We compute critical
Carbon-Oxygen and Helium core masses to determine our lower limit to PI
physics, and we provide two equations for $M_{\text{core}}$ and
$M_{\text{final}}$ that can also be of use for binary population synthesis.
Assuming the H envelope falls into the BH, we confirm the maximum BH mass below
PI is $M_{\text{BH}} \simeq 93.3$ $M_{\odot}$. Our grid allows us to populate
the traditional PI gap, and we conclude that the distribution of BHs above the
traditional boundary is not solely due to the shape of the initial mass
function (IMF), but also to the same stellar interior physics (i.e. mixing)
that which sets the BH maximum.
