When projecting the horizontal or nearly horizontal support enforcers or blockers
into object layers, the projection may fall on a layer above or below the layer
where it should in case the nearly horizontal support enforcer or blocker
triangles are intersecting the slicing plane of one of the object layers.
Due to numerical issues, projection of the support blocker or
enforcer triangles may not fall to the same side of the slicing plane
as when slicing the object. To make the projection robust, horizontal triangles
are newly projected to both the layer below and above if they are close
to the object slicing plane.