Elements Intersected by the Cut Plane
In a plan view, Revit uses the following rules to display elements that are intersected by the cut plane:

These elements are drawn using the cut line weight of the element category.
When the element category does not have a cut line weight, the category is not cuttable. The element is drawn using the projection line weight.
Exceptions for the display of elements intersected by the cut plane include the following:

Walls shorter than 6 feet (or 2 meters) are not cut, even if they intersect the cut plane.
The 6 feet (or 2 meters) are measured from the top of the bounding box to the bottom of the primary view range. For example, if you create a wall whose top is 6 feet above the bottom clip plane, 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.