I think that the compass reading was taken at the centre of the house to avoid deviations due to metal and to confirm the facing direction of the front door.
Usually, you measure the facing direction of the door standing in your doorway.
You can measure the location of your front door from the centre, which is useful if you use the pie chart or other applications derived from your horoscope (which are not part of Diamond Feng Shui).
The house still faces SW2/3 even if the door is located in the West sector. The stars of the West sector will be more dominant than the stars of the facing direction.
