Dittos to what Flatlander said.
Remember...our bodies are not all the same....thus.....we will not all anchor the exact same way.
For me....I've got big hands and a big, bulky thumb that gets in the way when I shoot split.
Shooting three under gets the thumb out of my way.
If the goal is getting the arrow to the right spot.....you can anchor by your ear if you want. Who cares what normal is!!
Best to ya!