FNW,
It's your statement that's rubbish, not the pilots!
Having the observer behind the pilot means that both he and the pilot can have eyes on the target, search area etc. while the front seat observer uses his very capable and expensive camera to view, search the area. The only down side of this is the rear observer or pilot will need to talk the front observer onto the target, search area.
Left side rear observer means a lot more communication with the pilot to achieve optimum position as well as having only one set of eyes looking out over the target or search area. The front observer is able to see the area in question and get the camera on target a few seconds quicker then his eyes will spend most of the time in the cockpit searching the screen.
Ask yourself why more and more of the Police Units are going over to the right?
Whenever.