XP earned

I may be stupid but i dont understand why do i dont earn all the XP i won to research a plane and it Can be a difference of 500xp by game.
I research a rank 6 with a 7. I’d think it’s because of the fact that i research with a higher rank but it doesnt make it with an other plane what is premium.
By the way i use mirage 3e for a f86 and i havent looked if it’s same in arcad.
Has someone an idea ?

Look here under “Multipliers”, the table to the right.

thank you very much