Coffin of Itib (Jt-jb), a high-ranking Hathor Priestess, 1919-1818 BC. Painted wood. Assiut, Egypt. © Ruhr Museum, Essen, Germany. Photo: Rainer Rothenberg
The Eye of Horus or Udjat was at the same place where the head of the mummy was lying – a bridge to the beyond, so the deceased could see the rising sun. This coffin of wood was put in a sarcophagus of stone.
The artist was free to design what he liked, based on his aesthetic view. No rules, it simply had to look good. Hint: the copy always starts on the side where the birds are looking to.