Because no one knows what the algorithms actually are, there's no way to exactly answer your question, but maybe this will help. Just keep in mind there are lots of factors in play and this is a way simplified version.
Author X, Caitie and Phoenix have sold enough to potentially make it on the list. In terms of how many books each has sold over the last few months, we'll make it easy and say Author X has sold more than Caitie who has sold about the same number as Phoenix.
Scenario: Author X is on the chart. Caitie and Phoenix are not.
Author X doesn't sell any books for 2 days and goes to #60,000 in rank (because rank is more "in the moment" and based less on historical sales). Caitie sells 5 during those two days and is now ranked at #15,000. Author X drops off the chart and Caitie jumps on. Then Phoenix sells 8 books and is ranked #10,000 and she jumps on and pushes Caitie off.
Author X sells another book. Her rank goes to #35,000. But Amazon looks at it as Author X selling again, and she's still sold more than Caitie or Phoenix in actual numbers, so back she goes on the list, pushing Phoenix off.
Then Caitie sells 5 more books. Now she's sold the same number of copies total that Author X has and her rank is now #7000. She leapfrogs ahead of Author X on the list. Author X will now need to sell more copies than Caitie to pass her on the list.
Author X sells 7 copies, but she's starting from a rank of #35,000, and that just pushes her rank down to #8000. But it's 2 more books than Caitie's sold, so she gets on the list ahead of Caitie. Since Caitie's still doing pretty well, she may just lose a rank or two on the list rather than being pushed off completely. But Author X is ahead of her even though Caitie's rank is #7000 and Author X's is #8000.
So since you can't influence how others are selling in relation to you, you can't really game the system or do anything to advance in rank other than sell a lot of your own books quickly and consistently. That's why all advice comes back to doing what you can to promote your books outside of Amazon and get buyers to come buy them.