"Walls shorter than 6 feet (approximately 1.83 meters) are not cut, even if they intersect the cut plane.
The 6 feet are measured from the top of the bounding box to the bottom of the primary view range. For example, if you create a wall with a sloped top face, when the top of the wall is 6 feet away from the bottom of the primary view range, the wall is cut at the cut plane. When the top of the wall is less than 6 feet, the entire wall shows as projection even where it intersects the cut plane. This behavior always occurs when the Top Constraint property for the wall is specified as Unconnected."
The below image (from the help files), is doing a great job explaining the functions of the view range, and the cutplane bahavior: