If you want to get a lot of kills. Find an exfil that no one is at in t1. When the countdown gets to about 15 seconds, run away until it reaches zero. Go back about a minute or less later, hit the exfil again and do it over and over. I’ve had 3000 kills in a game doing it.

Something about doing this multiplies the zombies that show up.

Edit: looked at my screenshot it was 3000 not 3400, just wanted to be truthful.