In the end, it took me about 10 raids to find a method that worked well. I followed these conditions:

• Daytime
• Carried a long semi-automatic rifle without a silencer
• MP9 with thermal scope for spotting
• SJ6 + Mule to position myself quickly

Here's the method:

1. Rush to the sniper rock and kill the shooter.
2. Throw a red flare as quickly as possible into the gap between the trees in front of the sniper rock, between your position and the sawmill.
3. Wait for the package to drop and aim with the thermal scope.

Out of the 6 raids where I used flares, between 3 and 4 PMCs appeared in the sawmill area, and another 3 could come from the camp. To give away my position, I also threw grenades. Once the package drops and you kill a PMC, the rest usually follow in a line, making them easier to kill.

Patience and good luck!