三衣(tricivara)

阿弥陀佛！
北传汉传佛教的三衣（安陀会（五衣），郁陀罗僧（七衣），僧伽黎（九衣））这三衣都是披着于身上，而且大小长短都是差不多一样。但藏传佛教的三衣(shemdab（五衣）,chogu（七衣）,namjar（九衣/大衣/祖衣）)与南传佛教的三衣(antaravasaka（五衣）,uttarasangha（七衣）,sanghati（九衣）)的披着法都是一致的。他们都是把五衣当下裙来披着的，只有七衣和九衣是披在身上，然而他们的五衣和七衣是单层的，九衣是双层的。若五衣七衣是双层则九衣须四层。所以想弄请问到底安陀会是应披在下身或上身？
Tricivara is so call as the triple robes of the sangha members,namely(antaravasaka（五衣）,uttarasangha（七衣）,sanghati（九衣）) in the theravada tradition, （安陀会（五衣），郁陀罗僧（七衣），僧伽黎（九衣））in the chinese mahayana tradition,(shemdab（五衣）,chogu（七衣）,namjar（九衣/大衣/祖衣）). In the tradition of the chinese mahayana tradition this triple robes is almost of the same size and are worn over the body from the shoulders to the ankle area. However, in the tibetan vajrayana mahayana tradition and the theravada tradition they wore their shemdab(tibetan) or antaravasaka(theravada) from the belly area to the ankle, and the chogu or namjar(tibetan) or uttarasangha or sanghati (theravada)wore it over the shoulders to the ankle area, which obviously that the antaravasaka is smaller in size than the other two robes so that it can be wore over the belly covering to the ankle. So why does the chinese have three robes the same size and wear the antaravasaka over the shoulders covering to the ankle just like the others two robes? And also antaravasaka and uttarsangha should be made one layer of cloth and sanghati two layer, or antaravasaka & uttarasangha is double layer then sanghati should be four layer where this sanghati should always of twice the layers than the first two robes.