I feel like I have been making tremendous progress just sticking with the basics in the Largo stage.  I keep watching the videos, and I seem to notice things missed previously.  My range is still low, but the sound is so much better.
What I am noticing is the feeling that the lips are vibrating more freely.  However, I also feel small volumes of air becoming trapped between the teeth and the lips (primarily upper).  I used to think this was related to unneeded resistance at the aperture, i.e. tight lips, but now I am wondering if this could be a sign of increased lip relaxation.  I notice this mostly when doing the lower pitch singing C exercises.
Should I be concerned or is this a good sign?