I don't know about MPG but I like the 16 tooth. It is cheap and easy to do. If you don't like it, just switch it back. There might even be someone on here that has one that they don't want and will sell cheap.
I would like to see a shot from the rear. I take it that you tried turning the pipe which would make it go up and down? Did you send the photo to Yosh? I would do that. Maybe that one pipe is screwed up from the factory.
Write back this:
(1). Are you the first owner of it? 10th (2). Where do you live? Spain (3) When have you been using it? Only in winter. (4)Does it has any dent on it?....Many.