  In this paper, a "centrality" estimator based on flattenicity ($\rho$) is
studied in proton-led (p-Pb) collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using
PYTHIA 8 Angantyr. Although Angantyr is still under development, the existing
implementation is enough to study the particle production in systems where
medium effects are absent. Firstly, ALICE data on pseudorapidity distributions
as a function of the forward multiplicity (V0M), as well as transverse momentum
distributions of identified particles in non-single diffractive p-Pb
collisions, are compared with Angantyr. Secondly, the average number of binary
nucleon-nucleon ($N_{\rm coll}$) collisions for different "centrality"
estimators are compared. The studies include the following "centrality"
estimators: V0M, $\rho$ and midrapidity multiplicity (CL1). On one hand, the
"centrality" dependence of $\langle N_{\rm coll} \rangle$ for the $\rho$
selection shows the smallest deviations ($<8$ %) with respect to that obtained
using impact parameter $b$; on the other hand, the V0M and CL1 yield huge
deviations (up to a factor 2) with respect to the results using $b$. The
particle ratios and nuclear modification factors ($Q_{\rm pPb}$) as a function
of $p_{\rm T}$ are also studied. The proton-to-pion ratio exhibits a flow-like
peak at intermediate $p_{\rm T}$ (2-8 GeV/$c$) with little or no "centrality"
dependence for V0M, $\rho$ and $b$ selections. The kaon-to-pion ratio as a
function of $p_{\rm T}$ is "centrality" independent for the same selections. On
the contrary, for the CL1 class the ratios exhibit the typical behaviour
associated with hard physics. Regarding $Q_{\rm pPb}$, a peak at intermediate
$p_{\rm T}$ ($2-8$ GeV/$c$) for different particle species is observed when the
"centrality" is obtained with $b$ or $\rho$. The observed features diminish for
the selections based on V0M and CL1.
