Have you noticed any variation in torsional vibrrations with different sorts of strings, particularly gut strings? When I had my violin adjusted for use with gut strings, I felt this might be the case. You would need presumably to assess the torsional flexibility of different strings. I would have thought a steel E string particularly inflexible, in contrast to a gut E. I have also tried using nylon (harp) strings, which are not good, particularly on high notes, but at least my nylon E string doesn't break, and is easier on the fingers by not cutting in to them!