It think this is something I put forward, and I think I kind of disagree a little with Sylvie's take here. I definitely put forward that we are talking about centers of the Self, which may not be Buddhistic in concept (ie, you would not teach "this is where the Self is"). I am describing where people in a culture locate the sense of Self, and this is reflected in the way a combat sport is scored, I argue. When you slap someone in the face, you are in a way "striking their Self". The face represents the Self in many symbolic ways, varying between cultures. A slap in the face with feel like it is insulting or injuring the Self differently in Japan than it will in Saudi Arabia than in California (I suspect), also depending on who is watching. And in the 18th century, perhaps much more so. It's not wrong to say that the Self is in some regards located in or on the Face. It's where we get phrases like "losing face" or "gaining face". There are other locations of the Self. The Heart for instance is widely regarded as a Self center point. Punches to the heart don't really seem to mean that much, but spikes driving through the heart, for vampires for instance, are seen as penetrating the core "Self" of the monster or person. And of course pangs in the heart, "heartaches" are some of the firmest centers of Self we talk about. I assume that this also varies between cultures. We have other centers of Self like the brain, or the head. Cutting off someone's head is in a way severing their Self from the rest (the face is up there too). But all this is to say is that in the arrays of Self centers, it strikes me that the Thais retain a more traditional location of Self in the gut. In English we have things like "gut feeling" and "you've got a lot of guts!", but traditionally this center of the Self in the gut, the spleen, was much stronger. In Ancient Greece this was a very strong location of Self (not the only one, but a core are vital one). My arguments about Thai Muay Thai scoring are that knees and kicks to the torso score higher because they culturally are read as hitting the Self, and injuring or weakening it. And that this is a traditional way of looking at the body. And that Thai audiences literally, affectively, experience such hits much more powerfully. They can "feel" the blows there in a way probably westerners don't. In the West it seems that these senses of Selves have migrated higher. We've lost the gut center more or less (a good gut punch and double over will still mean something severe, but on a daily basis we don't deposit our Self there much), and experience our Selves much higher. In the heart sometimes, but almost always in the head. We in the west lead with our head. And, it corresponds, it's why blows to the head and face (hey, we have a whole app that rules the world called Facebook), are scored so highly. We empathetically connect to fighters, and as audience experience blows or even touches to the head with more impact. I think we've lost some of the body mapping that allows Thais to experience lower torso strikes as much more substantive.
At least that's my thinking on it.