[TheSaxRunner05]

It goes off of the "AAA equivalency" when you finish a song. Only your top 15 AAA equivalencies count towards your level. 15-19 goods isn't great for rank scoring purposes, especially if any misses or boos are in there too. There is exponential decay on AAA equivalency, so it's usually best to go after scores you can SDG (single digit good). Try getting 9 goods or less on songs between 22-25 difficulty and it should see improvement.