Am I correct in understanding that if I use Avios to upgrade I'll get the Tier points and Avios awarded based on the class I paid for (rather than upgraded to), and that this is the same if you use a GUF to upgrade instead of the Avios (via BA). However, if you book via a TA, and use your GUF there, you'll actually get credit for the class you fly instead?

I may be assuming this because of mis-posted TP's last time I used A GUF via TA.

Can't seem to find this answer which is odd because I'm sure it's been discussed. Apologies for repetition.