  The quantum field theoretic treatment of inclusive deep--inelastic
diffractive scattering given in a previous paper \cite{BGR2006} is discussed in
detail using an equivalent formulation with the aim to derive a representation
suitable for data analysis. We consider the off-cone twist--2 light-cone
operators to derive the target mass and finite $t$ corrections to diffractive
deep--inelastic scattering and deep--inelastic scattering. The corrections turn
out to be at most proportional to $x |t|/Q^2, x M^2/Q^2, x = x_{\rm BJ} {\rm
or} x_\PP$, which suggests an expansion in these parameters. Their contribution
varies in size considering diffractive scattering or meson--exchange processes.
Relations between different kinematic amplitudes which are determined by one
and the same diffractive GPD or its moments are derived. In the limit $t, M^2
\to 0$ one obtains the results of \cite{Blumlein:2001xf} and
\cite{Blumlein:2002fw}.
