I'm pretty sure this has been done before but never understood why. I was just studying Hoefler engraved text and noticed the O wasn't a perfect ellipse as marked in the image below. The overlay on top in yellow is the ellipse and the bottom in brown is from hoefler text. Is there a reason why they do this? If you look at the
gif as seen here, assuming its to make up for width optically and even if I pulled the side anchors it looks off in the corners. Not to mention the anchors on the side are not center aligned for the O in hoefler's version, its like it's been pushed up a little. The green stroke aligns with the anchors from the brown text and the orange stroke aligns with the anchors on the yellow ellipse. Maybe I've over analyzing this but I'm kinda curious why its off centered and it's not an ellipse.
Thanks.
Edited image cause the first one was the wrong image.

Thanks
Comments
You ask why the letterform isn't a perfect ellipse. I might respond by asking why you would expect it to be? The letter O is seldom a perfect ellipse. Even in a geometric style of low contrast type such as Futura, the O is adjusted for optical reasons. In most styles of type the shape varies not only for optical purposes but also to give some liveliness to the form: pure geometry tends to look dull and static.
With regard to why the optical centre of the letter might sit slightly higher than the geometric centre — by raising the extrema of the sides slightly — this is for the same reason that the crossbar of the H sits slightly higher than the mid-height of the letter. Whether as a result of optics or experience, we tend to perceive geometrically centred vertical features as lower, so they are raised slightly to compensate. The same adjustment is observed in much art, and also in how we frame pictures or arrange text on a page: the bottom margin is larger than the top margin.