  With the semiclassical Landau-Vlasov transport model we studied the stopping
observable $R_E$, the energy-based isotropy ratio, for the
$^{129}$Xe\,+\,$^{120}$Sn reaction at beam energies spanning 12$A$ to 100$A$
MeV. We investigated the impacts of the nonlocality of the nuclear mean field,
of the in-medium modified nucleon-nucleon ($NN$) cross section and of the
reaction centrality. A fixed set of model parameters yields $R_E$ values that
favorably compare with the experimental ones, but only for energies below the
Fermi energy $E_F$. Above $E_F$ agreement is readily possible, but by a smooth
evolution with energy of the parameter that controls the in-medium modification
of $NN$ cross section. By comparing the simulation correction factor ${\cal F}$
applied to the free $NN$ cross section with the one deduced from experimental
data [Phys.\ Rev.\ C\,{\bf 90}, 064602 (2014)], we infer that the zero-range
mean field almost entirely reproduces it. Also, in accordance with what has
been deduced from experimental data, around $E_F$ a strong reduction of the
free $NN$ cross section is found. In order to test the impact of sampling
central collisions by multiplicity an event generator (HIPSE) was used. We
obtain that high multiplicity events are spread over a broad impact parameter
range, but it turns out that this has a small effect on the observable $R_E$
and, thus, on ${\cal F}$ as well.
