Due to the Oberth Effect, it is most efficient to accelerate a spacecraft along its orbit at or as close-as-possible-to periapsis, and decelerate within close proximity to apoapsis. But all discussions of this seem to be centered around pure tangential orbital acceleration, for example performing transfers within the same plane or reducing speed to allow orbital re-entry.
Does the same logic apply to non-tangential maneuvers, say, adjusting orbital inclination?
Assume we have two spacecraft in stable orbits of a planet that wish to rendezvous, and that these two orbits that are not co-planar. One must perform a transverse engine burn to adjust its own inclination to match the other.
At two points on each orbit, the orbital planes intersect. It is at one of these two points that acceleration must be applied to align the orbits. Regardless of whether this maneuver is performed at the ascending or descending node (defined by comparing their individual inclinations relative to the equator of the planet), at least some of the acceleration will be against the spacecraft's actual velocity at that time, because the goal is to reduce the relative inclination. Because of this, does the Oberth Effect make it most efficient to perform this maneuver at the node closer to apoapsis since the vessel's speed will be lower than at the opposing node?