SwissFrank, Alembic's adustment method is so different that a lot of times, they can be loose as someone gave up trying to figure it out.
It's simple and ingenious.
First, there's no springs or foam under the pickups.
So, you unscrew the two screws that are on top of the pickup shells to free the pickups. Then with an appropriate Phillips screwdriver that can reach through the holes, you screw in or screw out those two screws that are beneath the shells to set your heights. Once you get the heights where you want them, then re-tighten the screws atop the shells to snug them in place. It's that simple.
A few field notes:
Snug is good enough. Think valve-cover gasket snug, not tighten it till you grunt. Tighten the visible screws down HARD and you may very well crack the plastic shells.
Remember these are low-impedance pickups, and their is no 'right' answer for your heights. If you want to run them right below the strings, you can do it, provided your playing technique allows for it. You will hear a change in tone as they get closer or further from the strings. Not a big swing, but as they're not high-impedance, the magnets aren't strong enough to introduce any magnetic damping as would happen with high-impedance pickups, especially hot ones.
And you can fine tune this further: Take the back plate off the electronics cavity, and in an amongst the pots you'll see two blue boxes with a white adjustment that uses a tiny blade screwdriver. These are adjustable gains for each pickup. Crank your balance to the middle stop and you can set your blend via those two controls.
The circuitry allows you to essentially adjust pickup heights for tone, then the blue preamp boxes allow you set relative loudness of each. A brilliant facility rarely found in other makes.
