Hi! There are actually many factors that can contribute to the amount of rewards you earn and is not just based on your own individual Win Streak. As can be shown here:

Winning Streaks allow players to claim extra rewards but they are determined based on the winning streak your opponents manage to earn, as well as the result of the three battlefield. The battlefield that wins the event will receive extra rewards in comparison to fields that did not. Many factors contribute, terribly sorry for the confusion and I hope this helps!

~Jib

Jib Edit: Please ask if you have any questions, I will try my best to help =p