You are wrong here Shylark...
Rigth from the info when you go to halls BF:
" Effects increasing the valour received in battle do not apply in the Tallaar's Halls. If you are still under effect of any Valour Elixir after completing an instance, then the amount of valour rewarded will be doubled."
This is 100% how it works, folks with valor pots tend to use them around fight 15 or so, if they are in top 5 to get double the bonus valor. Much better ways to use them, but valor pots drop from chests now, so a lot of people have a lot of them.