[Battleground] Scoring system

I played 5 matches in total. The first was on the first day of release and I lost. Subsequently, I came in 1st 1 time, top 4 3 times. With 4 wins and 1 loss, my rating went from starting 4000 to 3600+. Something is quite wrong with the first match when many players were playing - I distinctly remember that loss resulting in a loss of more than 300 points. Please investigate.