You will hear all kinds of stories on exactly where to mount a fan in the fridge, but at the end of the day the whole point is to circulate the cold air being generated into the box, exactly as a residential fridge does. The air is constantly moving so the food is more consistent with no cold or how spots.
My fan is not mounted on the fins because all that does is single out specific places to draw the cold. Mine circulates the air clockwise in the box, and that naturally draws cold air off the entire assembly and draws the warmer back up to re-cool.
My fan is wired to shut off when the door is open just like a residential. Depending on which make and version the fridge is you may or may not be able to wire it to operate that way.
