As one idea leads to another, I´ve been exploring the moai head design.
It seems to me that these statues were done to be seen from this angle, so, it shows a true superhuman character, they are so old that is near impossible to know how much they have been eroded, and seen from another viewpoints shapes and proportions look somewhat incorrect, I think thay wanted some kind of anamorphism, and most probably the rear part was not visible to worshippers or whatever.
Gothic sculptures often show strange and winding poses for horses, lions, humans, etc. the aim was to show the full action from any viewpoint, and, usually, from a lower viewpoint, so, artists had to think about how to design a figure wich looks correct in these conditions.
Also, we know the columns of the Parthenon and other antique buildings were designed to equal the visual distortion introduced by its size to the human eye.
So, ancient artists were masters of geometry, and the geometry of this head is a masterpiece and probably the portrait of a true human ancestor.