Hig, I have not noticed TH going down with nic level (with 100% PG for me), but it is highly reported as so on ECF. Long-term VG/PG studies may not yet be in place, but I am a better person for using less tobacco products. it could be similar to the "quality vs. quantity" argument, that is valid in so many other circles.
It could depend on a fragile mixture of hand to mouth action, TH, flavor, and physical
Jonesing for the nic. On top of this, I used to love to smoke. Now I love to vape!
As mentioned, I dropped nic level quite a bit when I found a device/delivery system that was pleasurable to me. Because I enjoyed it, I tried to lower nic levels with that combination, and no PG OD so far!