One important factor is how fast that 6 upvotes happened and from who. If it got posted and got 6 upvotes within a few minutes and that from "proper" accounts i

One important factor is how fast that 6 upvotes happened and from who. If it got posted and got 6 upvotes within a few minutes and that from "proper" accounts it is on the front page. If it has the same amount but it takes 30 min then not. At least from my personal experience.