Always fun to read these posts..........
Both type air bags will lift the rear to some extent but one will lift more based on concept and design.
Air bags INSIDE the coils primarily keep the coils from compressing by exerting force against the coils (outward, not up and down. Also why they "float" and are not attached to anything) , basically using force/friction to restrict movemement. This is why these type bags instruct you to inflate the bags BEFORE you place a heavy load on them. They aren't meant to "push the load up" so to speak.
Bags on the outside, the ones that replace or go where the bumpstops are located, only come into play when the spring compresses to a point that the inflated pressure of the bag is sufficient enough to "impact" the load. By design, these type bags will generally "lift" the rear higher without any load..........
I'm sure it can be explained better