You might want to take a read through this. Most of what you're talking about is the Negative Pressure Air System.
In short...in the gun, how much gas is expended by each shot is determined by the length of the barrel, the weight of the BB, and fine tuned with the floating valve spring and to a minor extent the weight of the floating valve. In the mag it's the ability of the main valve to flow gas into the guns system. It's all a balance...you will end up with a messed up gun if you used (for example) a really light spring and a heavy float valve.
If you want a really good look, and chance to fiddle, take a TM Hicapa and closely examine the movements of each part. When/how/what causes each part to move, etc...