Okay, firstly, you take the total number of rounds you have won over the course of the four BTTB tournaments. In my case, it would be 22. Then you take the total number of rounds you have lost in the four BTTB tournaments, 17 for me, and add four, which would make 21. Then you divide the number of wins by the number of losses plus four, which in my case would be 22/21, which give your score. For me, my score is 22/21 = 1.047619048. You can also do the same thing for the four different tournaments. For BTTB4, I won 6 fights and lost 5, giving me a BTTB4 score of 6/(5+4) = 0.666666666.
I see... So why the +4?
You got my vote for RA2 Wizard. Always and forever.