  In this brief note, we confront our results on diffractive photoproduction of
$J/\psi$ mesons with the putative gluon shadowing ratio defined as $R_g=
\sqrt{\sigma(\gamma A \to J/\psi A)/\sigma_{\rm IA.}}$, where $\sigma_{\rm IA}$
is the result in impulse approximation. Building on our earlier description of
the process in the color-dipole approach, where we took into account the
rescattering of $c \bar c$ states only, we demonstrate that the inclusion of $c
\bar c g$-Fock states improves the description at small $x$ commonly associated
with gluon shadowing.
