Hey folks. Hopefully the hive mind can help me figure out what's happened to my scene...

So I'm trying to create an Ambient Occlusion render pass for a big, funnel/whirlpool shaped smooth mesh and sphere (first pic), as viewed from a moving camera. I followed this basic tutorial from the web, and I get strange results (second pic). This is the result after I crank up the spread in the mib_amb_occlusion to 50 instead of the default .08 (which just produced whiteness).

Now, I have to mention that my scene objects are really massive; the distance from the camera to the most distant surface point was measured as something slightly over 1 million (default maya units). In my attempts to make this scene "feel" larger, I've been upscaling things quite a bit, testing things...and I think this might have something to do with it. I've been changing attributes exponentially in attempts to see results...but this render result is baffling me.

I tried creating a fresh scene, and making some simple geometric shapes to test the procedure. It worked just like it said it would. As troubleshooting goes, I then determine it's due to variables in the scene with the whirlpool.

I'm running Maya 2013 as well...any thoughts on what these renders indicate?

EDIT: here's also a wireframe>render comparison of the model up close, as opposed to the first set (pics 3 and 4). The result doesn't change with camera distance.