I don't think that can work. Since when Fences in peak function. Your entire open application under it is just as a desktop area. I believe this is come back to Fences is a "Desktop" icons manager. So it only work on Desktop area. For peak to work, I think, not a Dev, so I am not really sure on this, what I observe, Fences freeze any open application that cover the desktop area and make it as desktop area. So any drag and drop from within the Fences to outside the fences it will drop on desktop not onto any open application that you can see.
Thank you,
Basj,
Stardock Community Assistant