can some explain Deal of the day Elixir?!

[Hook]

I bought "week long double xp " for my fox and so far it has been the biggest waste of 60 plat ever.

Situation:

My lv70 fox received a 3x daily Combo. I leveled for about 20 minutes at lost valley and noticed i was receiving 5/6 xp Per kill.
So i tought to myself to buy week long double Xp to make the free 3x even that more worth getting.

Problem:

I figured i was going to get 10/11/12 xp per kill??
But after a couple minutes of lost valley killing i checked and was only getting 6/7 xp per kill.
So the 60 plat elixir boosted my xp by ONLY 1.


What am i doin wrong or am i missing something.