  We study the impact of different Quark-Gluon Plasma expansion scenarios in
heavy-ion collisions on spectra and elliptic flow of heavy quarks. For
identical heavy-quark transport coefficients relativistic Langevin simulations
with different expansion scenarios can lead to appreciable variations in the
calculated suppression and elliptic flow of the heavy-quark spectra, by up to a
factor of two. A cross comparison with two sets of transport coefficients
supports these findings, illustrating the importance of realistic expansion
models for quantitative evaluations of heavy-quark observables in heavy-ion
collisions. It also turns out that differences in freeze-out prescriptions and
Langevin realizations play a significant role in these variations. Light-quark
observables are essential in reducing the uncertainties associated with the
bulk-matter evolution, even though uncertainties due to the freeze-out
prescription persist.
