Bending two notes, a wonderful exercise!
I just want to share how I made a huge leap in my bending abilities. :^)
I could not bend 2 notes together at all, as required in the level 4 songs. It always ended with a single bended note, the second hole ending blocked by my tongue.
I had taken the habit of pushing my tongue forward to initiate the bend while keeping the tongue on the harmonica, because keeping that contact was so hard at first. My tongue was quite tense, although I had succeeded in relaxing enough of its back to get some deeper bends (2" and 3").
To bend 2 notes, I had to relax the tip of my tongue, too, I struggled a long time, and suddenly I did it, and everything else became clear.
Now I can feel what bending really is! I can bend deeper, with good tone and at weak volumes. Sensations are much subtler, I can feel your hints about tongue location and your "wave" movement, which previously I tried to mimic and visualize, but actually failed (well, not totally since I had improved my bending, but it was very coarse).
For one full day I was unable to get this relaxed tongue directly. I had to keep on trying to bend two holes, and when I got it, focus on keeping that sensation across the harmonica. If I changed the key of the harmonica, I had to go through the adaptation steps again.
For me, this progress leap (through relaxing) came while trying to bend two notes. This is why I wanted to promote it here!
Great news ÉricD, thank you for sharing.