  Our goal is to gain new insights into the physics of wave overreflection
phenomenon in MHD nonuniform/shear flows changing the existing trend/approach
of the phenomenon study. The performed analysis allows to separate from each
other different physical processes, grasp their interplay and, by this way,
construct the basic physics of the overreflection in incompressible MHD flows
with linear shear of mean velocity, ${\bf U}_0=(Sy,0,0)$, that contain two
different types of Alfv${\rm \acute{e}}$n waves. These waves are reduced to
pseudo- and shear shear-Alfv${\rm \acute{e}}$n waves when wavenumber along
$Z$-axis equals zero (i.e., when $k_z=0$). Therefore, for simplicity, we
labelled these waves as: P-Alfv${\rm \acute{e}}$n and S-Alfv${\rm \acute{e}}$n
waves (P-AWs and S-AWs). We show that: (1) the linear coupling of
counter-propagating waves determines the overreflection, (2)
counter-propagating P-AWs are coupled with each other, while
counter-propagating S-AWs are not coupled with each other, but are
asymmetrically coupled with P-AWs; S-AWs do not participate in the linear
dynamics of P-AWs, (3) the transient growth of S-AWs is somewhat smaller
compared with that of P-AWs, (4) the linear transient processes are highly
anisotropic in wave number space, (5) the waves with small streamwise
wavenumbers exhibit stronger transient growth and become more balanced, (6)
maximal transient growth (and overreflection) of the wave energy occurs in the
two-dimensional case -- at zero spanwise wavenumber.
  To the end, we analyze nonlinear consequences of the described anisotropic
linear dynamics -- they should lead to an anisotropy of nonlinear cascade
processes significantly changing their essence, pointing to a need of
revisiting the existing concepts of cascade processes in MHD shear flows.
