Google has already said they don't pay attention to the code to text ratio. They extract what they need and ignore the rest. That aspect is not important in that sense.
Yahoo has a patent application in regards to visualizing a page layout without actually rendering it and explores ways to approximate the most important parts of a page from that visualization. This suggests, that if being used, placement in the code isn't as important as how it is visualized.
United States Patent Application: 0080033996
At least when it comes to local search, Google can segment a document based upon a visualization of that document as well. I don't think it would be a stretch to think that a visualization and segmentation of all documents could be used. Patent filing...
United States Patent Application: 0060149775
If indeed all pages are visualized then position in the code wouldn't matter. However, since pages can be segmented, then segment position within that visualization may since it would be easy to assign different importance to different segment.
Dave