I started this thread a long time ago. The reason for the problem is the location of the WiFi antenna at the front top of the screen, when the lid is closed the antenna is isolated by the Faraday effect. Unless you are sitting right next to the access point the signal will deteriorate. Future Surface Books may not have this problem if Microsoft moves the antenna, but for those of us that already own one the solutions are few and unsatisfactory:
- Leave the lid open
- Get an external WiFi adapter
- Connect the Surface to a Surface Dock or equivalent and use an external WiFi adapter or Ethernet connection on the docking device
Really bad UX design by Microsoft.