Calculate the needed angle for a 2.5 bar backshot using the HongHong system:
Click here if you don't already know it.
Then lower 2 angles and fire with full power (Credit to Sayo for showing me this).
In very upward wind you might need to lower more than 2 angles or walk a bit away from
the enemy after lowering 2. In wind that isn't so vertical you might need to lower only 1.
But the 2 angle rule is a good place to start.