The valve has a built in regulator, plus you have the bottle regulator (Flatline or any other). That's a dual regulated system which gives the best flow rate and regulation combination.
If you had two regulators feed an AGD valve, then it was triple regulated which actually hurts the flow rate. Each regulator acts as a restriction and must maintain about 200 psi pressure differential from input to output in order to give a good flow rate. For a level 7 valve to operate, you need about 350psi in the chamber which means 550 psi going into it. If you have a regulator between the gun and bottle regulator, then you need 750 psi feeding the middle regulator. As you can see, the numbers work for a level 7 mag to work with a triple regulated system.
However, if you use a level 10 bolt with a stiffer spring, then the chamber pressure may reach 500psi or higher. That would increase each increment by 150psi so your valve would require 700psi and the regulator feeding it would require 900psi feeding it. Now, a bottle with an 800-850psi output won't keep up quite so good.
A double regulated system works best because it holds the valve input fairly stable while maintaining flow rate. If the valve input has very little pressure change then its regulated output will be very consistent. The output change is a percentage of the input change at any given setting. A 4500 psi bottle output could change by 50 psi from full to empty(below the reg setting) which would cause havoc if this pressure was used to directly fire a paintball. Thats a 50psi swing for a 4200psi change. Now, the 50 psi change going into the valve regulator represents a very small change (approx 0.5 psi) in the chamber pressure compared to the 4200psi change for the bottle, so the chamber pressure change will hardly be noticed if at all.
Except for the Automag in front, its usually the man behind the equipment that counts.