  We investigate the asymptotic separation of the optical model potential for
nucleon-nucleus scattering in momentum space, where the potential is split into
a medium-independent term and another depending exclusively on the gradient of
the density-dependent g matrix. This decomposition confines the medium
sensitivity of the nucleon-nucleus coupling to the surface of the nucleus. We
examine this feature in the context of proton-nucleus scattering at beam
energies between 30 and 100 MeV and find that the pn coupling accounts for most
of this sensitivity. Additionally, based on this general structure of the
optical potential we are able to treat both, the medium dependence of the
effective interaction and the full mixed density as described by
single-particle shell models. The calculated scattering observables agree
within 10% with those obtained by Arellano, Brieva and Love in their
momentum-space g-folding approach.
