That's true, they do have that sort of control. The closest I've found to sinking a flat ride underground is to lower the land, build the ride, and then close it off with path - you can have a whoa belly or a tower coming through the path, it makes a neat effect, but the guests generally get confused by the path layout. Oh well.
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html