What's with the obsession of the heart position relative to stance? Granted if you get stabbed in the heart you are going to die, but that is true of a number of other places as well. Your stubbornness regarding this point is far exceeding your ingenuity in dreaming it up.
Speaking as a left-handed person in intellectual endeavors (writing, drawing, painting, eating etc) who practices all-physical endeavors (sports, Aikido, rifle marksmanship, European fencing) right handed, (this by the way I attribute to being taught most of my physical endeavors at a young age by my older right handed brothers and right handed father) if you practice the Asian style of calligraphy left handed it is extremely difficult. I had a Chinese friend of mine teach me some of the basic strokes for the calligraphy and found that when I tried it left-handed it didn't work so well. When I normally write, my left forearm rests on the desk and sometimes on the sheet of paper, this is almost impossible to do with the ink. When I tried it with my right hand, the characters actually came out better. So, without a reprimand from my friend for using my left hand, I naturally switched to the right. There is a method to the madness which may not be easily explained, nor even consciously known. This probably applies to the use of the sword as well. While the ideas put forth about military formations and social conformity make sense, your are unlikely to get a definitive answer to the question. And while, I may disagree with your heart position theory, you can even keep on believing that if you like.....
-joe