To the event's battle time calculation. PS: The more you lose, the higher your rating is

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It only counts your ACTIVE time.
Especially if you think the match is not having enough enemy, you can just suicide, and wait for a better time to respawn.

Also as a sidenote:

The more you lose, the higher your rating is.
So, you shouldnt care your team at all!

So that’s why I’m so high in rankings with my 20% win rate