3. Mystery unveiled:
Strings Do Stretch!!
...but... not in the same way, not of the same cohefficient... it depends on how are made and, first of all, from their gauge
We need to consider the many factors affecting our pure math calculations: the first is, of course, the string!
A string which is low twisted and maybe a bit stiffer because of rock allume, will stretch less than a soft high twist string.
So a first string made low twisted would help in maintaining our maths without having to increase the gauge, it would go in the direction of and equal tension profile.
Strings were of 3 kinds: chanterelles, mediums (mezzanelle) and basses. These were clearly different technologically, or there would be no meaning in selling them separately using this distinction....
So, chanterelles were a bit stiffer and low twisted, to help supporting the tension