I agree but expand on your "most Americans never see a tea pot", this
is an example of the context of many in the RSCDS in the UK, who are
out of touch with the population in general. While most of us, by our
age, upbringing, and context know what a teapot looks like first hand,
I suspect that this first hand experience is also lacking for the
majority of the U.K. today also.
To me, when I first heard it from Mary Brandon in the 1960´s, I wrote
it off as a bit of typical RSCDS esoteric trivia, and not particularly
useful term, and never used it in teaching, preferring "three hands
across". As to the particular grip, who ever heard of more then one
hand holding the teapot at the same time anyway.