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I've spent several minutes searching for answers with no success, but I figure someone here can slap me in the head for being a dunce and tell me the answer pretty quickly.
Why do some search results pages have the top blue banner position with a couple of sponsored links, and other search results have only the right side?
Think of it this way: there is an additional performance bar, focused on relevance as measured by CTR, that must be met in order for ads to be 'sent North'.
If none of that ads on the right meet this additional standard, in the moment of the search, then no ads are sent to the top.
A short time later, though, the circumstances may be different - and an ad may meet the standard and go North.