  Starting from the phenomenologically successful color dipole representation
of the diffractive structure function, we identify the dominant contribution to
the diffractive cross section at small beta. The beta dependence is calculated
taking advantage of the Regge factorization properties of the hard mechanism
which drives the dependence on the diffractive mass. We impose the unitarity
constraints on the $x_\Pom$-dependence and comment on the screening corrections
to $F_{2p}$.
