  In this communication I reconcile the kinematic method illustrated by some
authors~\cite{yang2018,vitali2018} in studying the impact of system and
suspension parameters on acoustophoretic separations with the statistical
method formerly proposed by Garofalo~\cite{garofalo2014,garofalo2014_2} and
lately extended to particle populations by the same
author~\cite{garofalo2017,garofalo2018}. The connection between these two
methods is established by (i)~reinterpreting the kinematic method in terms of
tangent space dynamics, and (ii)~transforming the dynamics in the tangent space
into the dynamics of the area elements. The dynamics of the area elements is
equivalent to the dynamics of the covariance matrix derived by moment analysis
and associated with the dispersion problem during microparticle
acoustophoresis. The similarities and the differences between the kinematic
based method and the stochastic method proposed by the present auuthor are
illustrated and discussed in the light of the numerical results for a
prototypical model of acoustophoretic separation. \keywords{Acoustofl
