  Observables in heavy-ion collisions are generally categorized into
centralities, which reflect an average over events within a range of impact
parameter including a wide variety of initial state configurations. A multiple
binning method using spectator neutrons within each centrality has been
previously shown to provide access to events with rare initial state
conditions. This work suggests an improvement in quantifying the difference
between standard centrality and spectator neutron binning towards accessing the
initial state properties. A selection of events with higher initial state
density at fixed participating nucleon number was observed to result in larger
final state particle production and smaller elliptic flow. The relative
difference between observables in centrality and spectator binning shows
reduced sensitivity for the observables dominated by impact parameter
fluctuations in initial state such as triangular flow. This property makes the
spectator binning method a good candidate to separate geometric contributions
from random fluctuations in initial state towards final state observables.
