People are working on the assumption that all faces are basically identical but with different proportions. As far as I know, this isn’t actually the case. Sure, we all have the same muscles but we don’t just see muscles… that would be creepy.
For instance, the brow is a very importand region. Some people have a prominent brow ridge(bone) and prominent orbitals (muscles) but these can relate in diffferent ways. They might have a high (virtically) ridge but the orbital might be lower. This creates a vally between the two. For other people, the orbital sits right on top of the ridge, but maybe a it will move, creating a vally, when the person frowns.
Another example is the one that I mentioned in the first post. There are creases and folds in skin - particularly around the eyes which have a genetic basis. We can agree on what is normal but Chinese people may disagree. There are differences that go beyond mere proportion.
Also, there are creases that appear in some faces but not others. Dimples are an example of ths. Some people have huge dimples even when they grimace, whilst others never get them no matter how much they smile.
Another example is sunken eyes. I remember a guy once told me that I had made a mistake in painting large depressions over a persons eyes. You can see him here:

But for me, those depressions were a part of the painting. I wanted to give the impression that he was a drug taker. People who take drugs sometimes end up with fast metabalisms. When a person has a fast metabalism, they burn lots of the fat that isn’t supposed to get burned - like behind the eyes. This leads to the eyes becoming sunken and this in turn leads to the creation of creases above the eyes which are otherwise not there at all.
So for me, there is no standard face. Some faces have features that others just don’t have - like Norway has Fjords and Irland has the Giants Causeway. It is NOT just a matter of changing proportions.
I am sure that people have done some in-depth studies on this stuff but it looks like I will just have to do a big load of googling to find them.