2x Elixirs supposed to work like this?

[Encryptions]

I start off with 3472 exp. I have 158% exp, 20% from pet 38% from gears 100% from base. Correct.
I complete a 1500 exp quest and end with 7342 exp.
7342-3472 = 3870. 3870 being the amount of exp I got from the quest.
3870 divided by 1500 is 2.58 which is 258%.
258/2= 129%. I start with 158% though.
I thought the 2x elixir will double everything like 2x exp day does? Meaning 158% would of been 316% giving me 4740 exp from a 1500 exp quest.
If its intended to just give 100% bonus exp can it be changed in the description?