Mark
You are not really missing anything. Although I do not think it was explained very well the importance of the distance from the chamber to the gas port, as it relates to the peak pressure in the chamber at extraction. This is the secret to the whole balancing act. It boiles down to this, the closer to the gas port the chamber is the higher the pressure in the chamber will be (at the moment of extraction), so, it is neccessary to slow down the bolt carriers rearward movement to allow pressure to drop. This is typically done by using more mass (heavier buffer). Depending on the size of the gas port in the bbl you are using, and the ammo, will dictate what weight buffer you need to have it run reliably. Sometimes it takes a little trial and error. If you look at the pressures in the chart, its clear that their is a huge differance in peak pressures between the differant gas systems, and all have less to do with dwell time than chamber to gas port distance. Hope this is helpful.
So, does this mean that mid length gas should be "more ideal" for a 14.5" barrel as opposed to carbine length, as stated above?