Horst,
If I well remember, mine was originally located in the cupboard below the chart table. I moved mine outside the cupboard for 2 reasons:
More midship location.
Sometimes I have metal tools in this cupboard, which could influence the magnetic field.
I have also one mounted in the wardrobe in the stbd cabin. I don't know which one is for the autopilot. I moved the one in the cubboard because my ST 4000+ didn't work well. Only after installing a rudder sensor and blind putting settings which I got from the internet, the function was OK.