  We study a geometry-dependent effect of long-range Coulomb interactions on
quantum Hall (QH) tunneling junctions. In an X-shaped geometry, duality relates
junctions with opening angles alpha and (pi - alpha). We prove that duality
between weak tunneling and weak backscattering survives in the presence of long
range interactions, and that their effects are precisely cancelled in the self
dual geometry alpha=pi/2. Tunneling exponents as a function of alpha, the
interaction strength chi, and the filling fraction nu are calculated. We find
that Coulomb interaction induces localization in narrow channels (large alpha),
and delocalization for sharply pinched constrictions (small alpha).
Consequently, an insulator to metal transition happens at an angle
alpha_c(chi,nu) <=pi/2. We discuss the implications of our results for
tunneling experiments in QH-constriction and cleaved-edge geometries.
