I'm puzzled. My best guess is that it is relevancy first, then equally relevant items are put in order of recency. But they also want diversity, so not sure how that plays a part?
I show up on first pages of search for most of my tags except the main one "bra", I'm not until page 11. I can't figure it out, but I am happy to show up for nursing bra, wireless bra, sports bra, etc.