Juro, I'm referring to a reduction in torsional forces during casting, not while working the popper on the water. In my experience, a small popper will spin on the water as a result of the leader having been twisted during casting. As the leader gradually untwists on the water, the popper spins in unison.
A higher diameter tippet (in relation to popper size) will resist this twisting during the cast more than one of a lower diameter. And by reducing the overall length of the leader, there is just simply less leader to twist, reducing the opportunity for any twisting to happen in the first place. My freshwater popper leader lengths rarely exceed six feet.