Hi, Michael,
I always try to stand or sit in the middle of the room in order to locate the 15 degree range. As I have seen with the mountain of my front door, the reading can also vary a lot depending on the daytime, electrical device etc. So I think that your intention to place it and to activate this area is even more important. I think Marie says sth. like that on one of the DFS CDs :-)
Love,
Astrid