Yes, I'd say those two have flatter heads than Lizzy. But then those big bumps on each side of the head behind the eyes are not as pronounced either. You know, they are similar looking to venom sacs on a hot snake.
Looking closer at Lizzy and it appears those bumps/nodules/jaw muscles? add to the triangle shape when more pronounced.
Lizzy, not the best photo for illustration. But those two raised nodules do cause a divot in the center. Hard to see here.
Mack here showing a flatter head.
This photo shows Etta's flat head pretty well.