  We develop the color dipole gBFKL phenomenology of a diffraction cone for
photo- and electroproduction $\gamma^{*}N \to VN$ of heavy vector mesons
(charmonium & bottonium) at HERA and in fixed target experiments. We predict a
substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA
range of c.m.s. energy $W$. The $Q^{2}$-controlled selectivity to the color
dipole size (scanning phenomenon) is shown to lead to a decrease of the
diffraction slope with $Q^{2}$ (which is supported by the available
experimental data). We predict an approximate flavor independence of the
diffraction slope in the scaling variable $Q^{2}+m_{V}^{2}$. For diffractive
production of the radially excited $2S$ states ($\Psi',\Upsilon'$) the
counterintuitive inequality of diffraction slopes $B(2S) \lsim B(1S)$ is
predicted, which defies the common wisdom that diffraction slopes are larger
for reactions with larger size particles.
