Another point of interest did you notice just about everyone portrait and the method and fashion was a three quarter view, in most all subject women portraits especially the eyes were down and away, look at all art history the majority are slightly down and the angle of the head.
This is why when you do take a three quarter view, you can walk to one side of the room to other stare at the portrait and it gives the illusion its following you. I have not seen the particular pose until recent I noticed it right away, a huge portraits of models a larger than life photo in a window, what the photographer did was had all the subjects slightly 3/4 view so as you see the photo approaching and you watch the photo the entire group seems to be turning and watching you as you look back, it was a fashion photo.
And most of the women beauty has a look of shy and timid, and if you notice in all portraits back then there faces were pale as they did not go out doors very frequent.
That is an excellent observation and may be the secret, they do appear that way,,,,,I had noticed that as wel alot of research went into that searching for the portraits with the 3/4 views and as I mentioned above if you notice for each portrait starts from left to center then right view. All my portraits I had ever painted were 3/4 view it was a challenge to align the eyes, the noise and chin, ,,,you would lightly sketch the lines for the eyes, the nose mouth and chin, in an oval,with the vertical and horizontal and vertical lines. to get the proper perspective and alignment of the entire face. a grid.