All answers are sorted from most votes to least votes. Answers with the same amount of votes are sorted oldest to newest. If anyone finds something that breaks this please show me.
Editing an answer will not move it lower.
If a new answer gets 1 upvote, it will be above all the zero vote answers but at the bottom of all the other 1 vote answers. That’d put it right in the middle of most threads. I’d guess that’s what you’re seeing. Do you have a specific post in mind?