Two factors to consider:
1. What is the second BG doing while you are shooting the first BG? Running away? Attacking? Taking cover? Freezing in place? What do statistics show to be the most likely action taken?
2. How much time does it take to transition from BG to BG? As the number of BGs increases, the time b/t the first BG shot & the last BG shot increases. Will you have enough time to engage all the BGs, regardless of ammo available?
Fights are chaos systems. Predicting chaos systems is slightly less achievable than herding cats.
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