  Using the colour dipole approach of the QCD perturbative (BFKL) Pomeron
exchange in onium-onium scattering, we compute the cross section for small but
hierarchically different onium sizes. A specific term dependent on the
size-ratio is generated. In deep inelastic onium scattering it appears as a
scaling violation contribution to the quark structure function near the BFKL
singularity. We find that the extension of the formalism for deep inelastic
onium scattering to the proton structure function provides a remarkably good
3-parameter fit to HERA data at small x with a simple physical interpretation
in terms of the dipole formulation.
