Don't forget the Geom module methods.
Geom.point_in_polygon_2D can be used to narrow down even further where the point is, once you know whether it's ventral (anterior) or dorsal (posterior.)
For instance, reference your view from the other thread, where you show the viewing cone(s) looking downward. Getting the 3 vertices of the horizontal conic section defines a triangular face that can be used with Geom.point_in_polygon_2D, to see if a point should be within the projected section (without regard to z position.)
Repeat the exercise using the vertical conic section, and if both return true, then the point is inside the viewing pyramid that curcumscribes the viewing cone.