If you have a systematic approach and you say you've been using for several months with no improvement. Then I would suggest that you are either not doing something right or doing something wrong (there is a difference). before you make a DIY embochure change see a good teacher. They can see how you are using your air for one thing. The other is to see what you are doing and how you are doing it. I find a lot of students really don't know how to practice for improvement. Just repeating something over and over won't lead to improvement.