Well, the areas furtherest from the cathode will see slightly less, proportional to the electrical resistance of the electrolyte. But, since the electrical resistance of the electrolyte is very low, that difference will be very low.
If the cathode is nearer to the work pieced then the variations will be greater.
I would expect the back side to look like it had been immersed with no current.
The cathode is 5mm from the sheet to be polished and the bath/rig does hinder a line of sight to the other side of the sheet. So its going to mostly polish just one side...?