What is a convention that egyptian artists used in wall paintings?

Although you did not provide answer choices, I believe the answer is that they depicted body parts in their most recognizable position. 

Some books said that they studied the human form to depict accurate proportion and that's not true. Instead, they painted art in a way to tell stories, nd that's why they painted what happened through out their lifes and so when they painted people they depicted body parts in their most recognizable position to keep a clear memory of how things happened.