Indeed. For two-way detection, the two ecliptics must be in the same plane. Or more accurately, the two ecliptics must be close enough to a common plane, where

Indeed. For two-way detection, the two ecliptics must be in the same plane. Or more accurately, the two ecliptics must be close enough to a common plane, where the common plane passes through both planets and "close enough" means within half a degree on Earth's side.