is your advice to play to 2 feet from a wall is right but I meant how to change the sound already in the oral cavity even before it gets to vibrate the reeds of the melody.
1) blow hot air (breathe ….) ….. This allows you to vibrate the reeds in the right height / intonation. The cold air instead is synonymous with velocity and so it might come out a sound forced.
2) Create a “sounding board” in the mouth a bit as do the singers ….. we will have a darker sound and rich harmonics …….
3) Think of singing the melody you are playing in order to facilitate our musical sensibility.