With all those various spheres and damper diameter holes, for any given Citroën model or even accross models, it is difficult to see at first how and why all these physical factors influence the suspension comfort.
To start with, these are the spheres originally fitted:
A sphere is only as good as the neoprene membrane that contains the pressurized gas. Occasionally, the interface between the membrane and the retaining plate inside the sphere is to blame for leakages, but usually any problem is associated with the membrane itself. Like anything that's under constant flexing, it'll break down over time.