Anatomical variation is a surprisingly ignored consideration for face tracking/facial mocap in tech and entertainment. Simplified anatomy diagrams are often accepted as universally applicable to all faces and few further questions are asked. The reality is: FACIAL MUSCLES ARE HIGHLY VARIABLE.
Currently learning chimpanzee FACS, chimpanzee anatomy, and making custom chimpanzee landmark diagrams. (Chimpanzee landmarks determined by Animal FACS group. Original research work by Lisa A Parr, Bridget M Waller, and Jennifer Fugate. See: Emotional communication in primates: implications for neurobiology )