Oh. The pilot only needs the first set of spherical coordinates to aim, the one which is nearer in time. I suppose you'd take the slope of that parabola for that. A second shadow reticle could certainly be shown though; the closer they are, the better the chance to hit, either because the curve more closely follows the target's path, or because it's flying away from you, at which point we're doing that shortest path jazz you were talking about earlier.

And conservation of momentum is a terrible law that binds and limits out physical world, and it should be revoked as soon as we're able to.