Sounds like you may have an expression on the position property inside of particular? When you do that and you duplicate a layer, particular takes the random seed from the layer order, so the 2nd layer will be in a different position.
A better solution is to create a null object and then alt-click on the position inside Particular and pick whip the position to the position of the null object. You can then move the null around with an expression as before but when you duplicate your particular layer, it will stay in the same spot.
At least that's a fix if I understand your problem correctly?