1) the back need to be on the same level as the front in composure
2) the back output need to be set to "player Viewport"
3 ) add a transform pass in the back composure to "Smode compositing watermark Pass"
4 ) in the front composure change the output layout to Fill and Key
5 ) in the Smode rig transfer the back composure into the Back Capture array
6) in the front reduce the size of the windows and Viewport
7) add a new node with the name back with a window and viewport: