I was thinking of this thread these days. Good that it was woken up.
My Xantia history was kinda frozen as I was directing all money to the new house and its (neverending...) list of things to buy.
However in the last months I've been working on it. I've replaced the 2 strut mounts (sphere support as citroen calls it), as one of them was in incredibly bad shape... I still can't believe my strut didn't pop up!
Anyway, being a noob at that job I spent a good amount of LHM and needed to top it again.
(Every time the strut came down as I was trying to make it through the mounting, it would spit LHM on me. How dare him?

)
I then needed to refill the tank. There I found the hack I created to "detour" the bubbles to the top of the tank which was just some piping (and needed to remove the filter).
I went ahead and cleaned the pump filter which was in bad shape, removed the hack and installed a bernie-registered version

of it with the return filter in place.
Well, again, the steering was so light I thought the wheels were on soap, even when idling. The ride was somewhat better but that can be because of the new strut mountings.
I still need to fix the lower arm bushings, which may be helping on the job of transferring potholes to my bones, some spheres and a good system clean.
What I recommend you to do is to use a section of transparent piping in the path to the pump, so you can see if your bubble problem is big or not.
I did that and then did the same on the return piping from the steering and that was the bubble feeder.
Putting the steering return pipe on the reservoir's top made the bubble flow decrease a LOT.
Regards,
Pedro Prado