Creating mannequin heads has been tough to nail down as a sculptor. They present a lot of problems with regards to a few things. First, I try my best to create features based on my reference photos as accurately as I can. This poses a major problem because mannequin manufacturers don't always scale or sculpt body parts according to reality. They tend to scale things based on a certain style or to allow clothing to be put on the mannequin in a retail store setting.
Why is this a problem for the realistic type of likenesses people request? For starters, an accurately sculpted head will have anatomy that doesn't line up with non-anatomically correct necks. This means the rear of a persons jaw or their ears will appear to be too far back on the head depending on how the head is attached.
Another issue is that wigs are more or less one-size-fits-all. If you scale a head down to look accurate on the thin necks, the wigs can be too large. They may sit loosely and need additional help to keep in place.
After several years of trial and error creating each head uniquely, I've decided to standardize the heads that I make instead. The new measurements are based on client feedback and by measuring features that have worked in the past and looked best.
This means that each head will have the placement of certain features that are the same for all of them, except the areas forward of the ears and below the center of the head. The neck diameter, head width and length will all now be uniform within reason. The ears will also be more centered as not to look strange if the person normally has ears that way in reality.
This will solve problems for both the clients who want aesthetically pleasing features. It will also make it easier to attach the heads with the least amount of work. In short it will make life easier for everyone.