It seems universally we make hand matzos circular and machine matzos square. I'm assuming the reason for square machine matzos is to distinguish them from hand ones and also because it is more economical to bake them in a cut up sheet of similar forms. (Please feel free to correct it if this is wrong.)
My question is, why are hand matzos circular? It seems sefardim and ashkenazim make them like this, which suggests this is a universal minhag of some sort. Are there halachic or midrashic or kabbalistic reasons why this is so?