Neck width ratio

[Futura]

Why did so many ladies' drafts set the back neck width narrower than the front?

The only exception I could find within my own collection of English tailoring books was Dellafera's "Jacket for Stout Figure". The back neck there was 1/6 scale plus 1/4" and the front neck 1/6 scale, in order to produce a shorter shoulder seam.

Morris made a big point of stating how important the relationship was between 1/6 scale less 1/4" for the back neck and 1/6 scale for the front neck in order to prevent a gaping back neck. This formula is used throughout his book, including the dress drafts.

It seems illogical and anatomically incorrect for a lot of people. It is at odds with virtually all dressmaking fitting advice I've read, including texts from the same era. How did this come about?

[Futura]

I should add that I realize that the shoulder seam can be (and frequently was) set further down the back, which results in a narrower back neck on the draft.

Judging by the sleeve drafting instructions Morris wrote, the top of the sleeve cap was supposed to be at the actual shoulder point? Unless I am completely mistaken. He never specifies the exact placement of the shoulder seam for the neck point.