The tractor pivot kind of looks like a versatile articulated 4wd. (Lol just scrolled up to the first post haha)
The first sensor arm should point in the direction of travel, either forward or reverse. Here is an example from a Stieger 4wd. In this case the first sensor arm points in reverse behind the steering joint like a tail.
The purpose of the second arm is to allow for movement back an forth in the radius if not perfectly on center. As you can see worn into the dust on the lower support.