[FrankJ]

Fig 4-8 shows the bumpers being perpendicular to the floor. You really can't tell if they are parallel from the figure despite what the blue box says. I have always interpreted that rule to mean you cannot have "cow catcher" bumpers. We have never had a reason to mount one end of bumper lower than the other or have anything other than rectangular bumper so we never tested the exact meaning.

Currently you can have several bumper segments on on a side each one slightly higher. having the net effect of an angled bumper. Now as dX approaches 0....