A final mistake is throwing the second ball behind the first, rather than inside.
I noticed in myself a need to orient, at the first mention of inside, and in this statement, I notice the “inside” I picked has the wrong reference frame. Not in use: “Inside” as body-side of the plane of the two outstretched hands and top-of-arc (/ center of Earth’s gravity); instead in use: “inside” is about the box circumscribing hand-hand-apex.
A single sentence, or two, on this orientation would clear things up for me in first read—to fit the clearly optimized smoothness of the introduction.
I like kneeling in front of a couch. Big area to catch the balls, they roll back into reach, and you don’t have to bend over to pick them up.