Stumpkiller: actually, I do wear glasses. In fact, I have a pair of "cheater" glasses I had made that focus at 3 1/2 feet, as the front sight was gettin' a little blurry. (And you can see the progression of my rear sight forward by the blanks put into old dovetails.) Put the lenses in a late 19th century frame so I can use them at primitive matches. The length of pull I like is 13 1/2", about 1/2" less than finger to elbow length. So you are correct about figuring an individual's initial length of pull, but other factors enter, including stance as mentioned above.
The rifle I mentioned w/ a short LOP was at an antique gun show & I didn't have a tape meassure: barrel musta weighed about 15 pounds, small bore & thin buttplate. Heavy barrel could lead one to think it was an over-the-log rifle, but that would put the lock next to my right ear: downright uncomfortable.