Tuning Newbie FX impact m3 help. At what reg do you stop shooting?

The FX manual says to never shoot your impact below "regulator" pressure. But they don't clearly say which one. Reg 1 or Reg 2? I sure hope it's reg 2 because that's what I've been going by. I shoot until my tank pressure is just above what I have Reg 2 set at. However, I just watched a video about tuning and the guy said to not go below reg 1??? I'm so confused. If it's reg 1, that would drastically cut down on the number of shots.

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