Next time you look at the front of the trigger block after you remove the bottle, at about 1:00 to the right of the fitting the bottle threads on you’ll see a grub screw seal.
Now go look just above the hand grip, behind the power wheel and you’ll see another grub screw seal(remember these are those are potential leak points. During the manufacture process, this tunnel is drilled out from one end of the trigger block to the other end, and is the main highway for the HPA to reach from bottle to plenum. Within the trigger block other pathways have been drilled out to tap into that main highway, which are pathways for regulators and for the gages to read pressures at.
That drilled out path is the tunnel that the 2nd reg taps into, the air passage way. You’ll also notice your first regs pressure gage is sort of tapped perpendicular to that tunnel path.
Your bottle is a 250 bar fill. The reg in front of the bottle drops it to say (example)170 bar. So 170 bar(way less than 250 bar in the earlier impacts) is pressure down that tunnel and into the 2nd regs cavity. A regulator is a valve, like a faucet. And that 170 bar is held there in place until you call for opening the valve, which comes with the trigger pull. The trigger pull releases pressure, and because the pressure coming from the bottle is higher than ambient, air will now move from cavity to cavity within the gun- make sense so far?
Your second reg(example) is set for 120 bar. From the second reg to the valve seat is 120 bar pressure. Trigger is pulled, hammer strikes the hammer stop, pulling the valve poppet seal off of the seat, releasing air up thru the transfer port and into the skirt of the pellet.
Whatever amount of air that got released in that moment in time gets replenished into the plenum thru a tiny hole where your front end cap beak resides in and tops off the plenum.
During the shot the second reg had opened for that moment in time and taken more air from the 170 BAR side of the first reg. The first reg, also in that moment in time, had also opened and allowed air in from the bottle.
The regulators washer springs are taking the place of your hands shutting off those faucets, and depending on how much you opened or closed the reg(setting the reg pressures), it only allows so much air in because the pressure differential closes off “the faucet”.
No high pressure uphill air(at the bottle)will enter another compartment divided by the regs, unless pressure is released downhill(pulling the trigger). If HPA does get by into another compartment divided by the regulators(the faucets), that means your regulator seals are compromised, and it leaks or creeps air(like a leaking faucet, ha ha)
As I’m typing all of this, everything makes sense to me, and I’m not sure if it will to you. I finished off my career as an HVAC and Sheet Metal trades instructor and duct design, pressure differentials, heat calcs, all that I would’ve busted out the dry erase marker and drew it all out. If I was there in front of you I would do the same.
To the impact aficionados, that have been around the impact for a bit, if I left anything out or if you want to break down my “splainin” even better, feel free to do so.
What would be cool is if I had just the trigger block, armed with a camera and flashlight, it would be easy to show the different tunnel paths within that block.
The impact is truly an engineering marvel of a gun
www.airgunnation.com 
. the 2nd reg will regulated that already regulated air into the plenum and valves. When the gun is fire, it will only see the 2nd reg pressure. Kinda common sense if you ask me.