On the debate about whether von tag (or whatever name you give it) should be held over the shoulder or with the cross below the collarbone, I cannot say what the old masters prescribed. Some have cited to them, but have not quoted the exact language so we cannot tell if their interpretations are correct.
However, this is a point where it might be helpful to repair to another martial art to compare what is done in a similar situation. Many kenjutsu systems have a posture, or kamae, similar to von tag/posta di donna (or what have you). It is usually called hisso no kamae regardless of how it is done. Whether the hilt is over the shoulder, at the ear, or below the collarbone varies from one ryu (or system) to another. There is no concensus among the systems about where the hands should be placed.
In those systems that use the below-the-collar version, in every video of actual cutting I have observed (I've looked closely at this, sometimes frame by frame over the years because of this very controversy), the swordsman raises the blade above his shoulder to the von tag position over the shoulder before issuing the cut. The cut is NEVER delivered straight from the breast as we saw in
http://www.youtube.com/watch?v=3fGlYAFvtbI . You can see this in the film Budo and in Soto Tanemura's video on the sword, for instance.
You can make of this what you want, but I strongly suggest that this evidence should not be ignored.
I also suggest that you who use the below-the-collar version try an experiment. Assign an unsuspecting student to test cut an object that requires some force to cut, like a pork shoulder. Let him start with the below-the-shoulder von tag. Film the cut. See if he doesn't raise the blade to make the cut.
Also, do another test cutting experiment. Take a pork shoulder and make the cut from the breast. Gauge the results on the target. Then make the cut from above the shoulder and compare the result.
