I have one tank that forms a room divider and it's pretty clear the openness makes some of the fish more skittish. I think this is also true of the 55 gal in front of the window. When it was young and going through it's algae phase, I blocked off the back with cardboard to regulate the sunshine. Now that algae is gone and so is the cardboard, the corys swim and hide like crazy every time they see me.
Anyway, if you think this is true of your tanks, it's another argument for covering the back. I like the idea of doing it with something easily removable.
jim