Still not sure that you are getting at?
Here are the gas port pressures on the different lenght of barrels at the gas port, and the gas port is sized correctly to deal with these pressures to get the bolt unlocking at the correct residual bore pressures so the spent case can be pulled cleanly.
Again, gas port size to created the needed bolt timing unlock with the amount of pressure at the gas port as the bullet passes, then you have buffer mass and spring tension as the final parts of the unlock timing math. So recoil spring lenght is determined by the depth of the receiver extension void, and the spring tension is dictated by the weight of the buffer in play.
As for why carbine cycle rates are more violent that say a rifle stoke, with the barrel gas port closer to the pike of the dwell burn spike, different ammo's (223 55Kpsi verses Nato 62K psi), you get more ammo pressure variances (wider swings) to the math of gas port pressure to the B/C, than a gas port much farther down the barrel. Also, carbine rigs weight less than a rifle rig, so your going to feel more felt recoil as well.
Hence rig set up for 223 ammo, in carbine or rifle will be about the same unlock speeds (felt recoils greater on the carbine due to the lighter weight), but when you switch over to 5.56 nato ammo with greater working pressure, it's going to speed up the carbine rig cycle rate more than rifle cycle rate, since the gas port is much farther away from the chamber on the rifle instead. Again, look at the pressure at the gas port for different barrel gas port locations, and the higher the working pressure at the location, the greater your going to get from variances off the base line standard pressures down the port.
So we never use a carbine buffer in a full lenght receiver extension, since this will case the back of the key to crash into the lower receiver at back of stroke (the the bolt face retracts back past the back edge of ejection port window), and we never use a full lenght 11.75" spring in a carbine receiver extension, since it will coil bind out before the buffer bumper can make it all the way to the tube back wall to allow a full stroke.
As for carbine 10.5" spring in a full lenght receiver extension (where you should be using a 11.75" spring), bad idea since the spring does not have the needed amount of preload to start with, and can end up with the bolt unlocking too soon isntead.
So simply, break the rifle down to upper and lower to start with. Buffer lenght and recoils spring parts are totally dependent on the receiver extension lenght in play, and have nothing to do with the upper receiver at all.
Now in the case of a carbine receiver extension with its needed carbine spring, and back to the upper receiver play on it, we can play with the weight of the buffer to bring the bolt unlock back into check if we are running into over function problems with the bolt unlocking too soon. Hence we have a rig set up for 223 ammo, but are going to run Nato ammo in with it greater pressure, or even MK262 with it slower burning powder that will increase the amount of gas port pressure. Here, we can increase the mass of the buffer to slow the unlock back down to normal timing.