OK, I admit it. My whole career as a singer, I have had teeth that didn't meet evenly, a jaw pulled to one side, stress on one side of my neck and an uneven vibrato. I can't remember a time when I didn't know there was a problem. I have spent the last 30 years trying to correct the issues, ever since David Smukler showed me just how tense my jaw was, at Banff in 1981. When your voice is off the rails, all you can really think about is how to get it together.
I have been taping and listening to myself a lot lately. The other day, I thought "I hate me 'n's'. They sound adenoidal and are too far back. What gives?" It turns out that after balancing my jaw and support so that they are centered in the middle of my body (not off to one side), releasing the neck, and making space for the upper register, I still have an issue with my tongue! I tend to retract my tongue on the left side, which makes all my singing too far back, and makes the "n" particularly off-balance. Now that the other issues have been more or less resolved, my lop-sided tongue has come to the fore.
I suppose the whole crazy cabal of tension began with thumb-sucking as a kid, and teeth that grew in off centre. If teeth are off, jaw will be off, and if jaw is off, then the tongue will also be off; but correcting the tongue without balancing the jaw was just not an option. I believe that these tension issues have to be resolved in a certain order, and that order depends on your particular development. It is like untying a knot. The last tension issues to resolve may be those closest to the larynx, and the tongue is particularly close, attaching to the hyoid bone, which in turn suspends the larynx.
If you can't release the tongue, you can't release the larynx. Bringing the left side of my tongue forward gives a whole new balance to the voice, and not just to the "n". I will let you know how it works out. In any case, just shoving the tongue into the "correct" position never worked for me. I had to untie the knots.