Here's some "theoretical" data we can compare against the actual measurements forthcoming.
I took the temps we have for the pure PG and VG boiling temps and interpolated temps from the mix ratios between them. I also did the same for our temps where nasties are formed from data posted here.
So this assumes that VG will boil at 554F with nasties at 420F and PG at 370/480F and so if you have a 50/50 mix you'll boil at 462F with the nasties at 450F. So these are numbers to test if it is fair to do linear interpolation for the mix temps or if something else is going on. There may be no truth to this whatsoever. The measurements will tell us about the boiling temps but we still don't know about the nasty formations. It could be that nasties still start at the lower 420F bound set by the VG or it could be that the VG is whisked away at a lower temp by the PG in the mix.
The Margin shown below is how many degrees of headroom we have in the interpolated values. It is interesting to note that by this we need at least 55% PG to stay in safe zone. In reality there is nic and flavoring that will add PG and/or water/other content as well.
Here's the table:
View attachment 654171
It appears you averaged the Boiling Points of the 2 components together to reach a theoretical BP.
From what I have been reading it is not that simple by any means. It started getting over my head real quick, but there is something called Raoult's Law that comes into play, and it gets down into the molecular level of things.