  One of the greatest uncertainties in heavy-ion collisions is the description
of the initial state. Different models predict a wide range of initial energy
density distributions based on their underlying assumptions. Final flow
harmonics are sensitive to these differences in the initial state due to the
nearly linear mapping between eccentricities and anisotropic flow harmonics.
The Trento code uses a model-agnostic approach by phenomenologically
parameterizing the initial state and constraining those parameters from a
Bayesian analysis. There the multiplicity fluctuations were determined by a one
parameter $\Gamma$ distribution. However, initial-state models arising from the
Color-Glass Condensate (CGC) framework lead to an initial energy density which
is outside the functional form considered in Trento and its later Bayesian
analyses because they rely on log-normal multiplicity fluctuations. We compare
$T_{A}T_{B}$ scaling (CGC-like) to $\sqrt{T_{A}T_{B}}$ scaling (preferred from
a Trento Bayesian analysis) and find that the $T_A T_B$ form together with
log-normal fluctuations is a reasonable candidate to describe the multiplicity
fluctuations but leads to larger eccentricities, which would affect the
extraction of viscosity in small systems.
