The height on a Xantia can be adjusted but as others have already said,
this is only possible on a flat ramp. The reasons for this are 1) you
DO need the weight on all four wheels, 2) You need to be able to move
the height up and down without the risk of being squashed (yes this has
happened) 3) The car needs to be level.
To set the rear height.
Have the car on a ramp with engine running
At the rear height corrector you will find a plastic link, this links
the height corrector to the anti roll bar link
On the anti roll bar link there is a M7 bolt (11MM head), loosen this
bolt and make sure that the clamp can rotate on the anti roll bar.
Using a screwdriver, lever the peg in the middle of the height
corrector back and forth, (Towards the rear bumper to go down and
forward to go up)
When the car is at the correct height, the anti roll bar adjustment
clamp will have followed it to the correct position.
Tighten the anti roll bar clamp (M7 bolt)
I cant remember what the height is, but the measurment is taken from
the rear of the back sub-frame mount.
It's worth pointing out that the height corrector will never go out of
adjustment on its own, unless someone has played with it, you may be
needing a new one.
Trust me I have fitted loads of rear height correctors on Xantia's, If
you have a Xantia you will need one, it's not a question of IF it's a
question of WHEN !!!!
Check out www.citroen-hydraulics.com for piccies.