I think I was thinking you meant having Fences on two screens, individually, but not in the middle.
Though I tested this, http://screencast.com/t/lgLi33DHtlI , I do see it on both monitors.
Are you attempting to use the Fences Pages feature? If you place the Fence over the edge of the monitor and are using the Pages feature, then swipe to see the next page, you won't see the other half of the Fence. My best suggestion would be to keep the Fence within the monitors boundaries and not outside of it. Then when you swipe, you have your Fences view able.
