  We study the interaction-induced connectivity in the Fock space of two
particles in a disordered one-dimensional potential. Recent computational
studies showed that the largest localization length $\xi_2$ of two interacting
particles in a weakly random tight binding chain is increasing unexpectedly
slow relative to the single particle localization length $\xi_1$, questioning
previous scaling estimates. We show this to be a consequence of the approximate
restoring of momentum conservation of weakly localized single particle
eigenstates, and disorder-induced phase shifts for partially overlapping
states. The leading resonant links appear among states which share the same
energy and momentum. We substantiate our analytical approach by computational
studies for up to $\xi_1 = 1000$. A potential nontrivial scaling regime sets in
for $ \xi_1 \approx 400$, way beyond all previous numerical attacks.
