AP is not usually installed by the boat builder. Rather, it is most often installed by the owner, well after commissioning of the new boat, sometimes not until a subsequent owner has the boat.
Therefore, there can be no "usual place", but rather, the location is found by thinking, where would you put it, if you had to find a place as far as possible from magnetic or electronic items that may cause/receive interference, all without requiring removal of joinery.
I have one in a tiny locker, just by my left hip, if sitting on the head, a second, newer one, visible up on the pillar between the front windows.