I think Morgano's diagram is spot on (you beat me too it BTW).
the reason the landscaping isn't accurate to whats on the plans, is because the proposed landscaping either wasn't ready, or the details were omitted. I found this out when i was trying to create my model (viewable via the link i my sig), there is a huge lack of landscaping detail on these plans.
If the elevation height was left as is, then people would be walking directly into the cobra roll/batwing elements.
On my model I have had to sink the land below the elements by at least 2.5 meters to make it work with the proposed track layout,
If you look at the size of the concrete wall, thats got to be about what, 7-8 meters high? Then if you look at the plans, the height of the roll is 17m from ground level, leaving a speculated area of 2 meters in the trench. You've got about 5 meters unaccounted for..