  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 is presented. A substantial
shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of
c.m.s. energy $W$ is predicted. 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). An approximate flavor independence of the diffraction slope
in the scaling variable $Q^{2}+m_{V}^{2}$ is shown to hold.
