So, for small teapots, including this one, Teaparker recommends I hold it with the index on the knob (see picture above), the Phoenix hand, according to Scott. This is how I then practiced it with my teapot.
In case I didn't feel comfortable enough, or should I use an even bigger teapot, then Teaparker advises to hold the handle with one hand and knob with a finger (index or middle finger) from the other hand (See on the left).
I now remember that Teaparker often told and showed us how to hold a teapot properly. I just didn't make this lesson mine for medium and big teapots. So, the pictures below (taken last year) clearly show the student (me, with my thumb) and the master.
However, thanks to the discussion that was triggered and the article I now wrote, I think this time I won't forget again!