The refers work more on convection type air movement. The refer will be more efficient with more air moving over the cooling unit.
You can restrict the area between the rear of the cooling unit and the refer cooling unit to make it more efficient and cool better. There should only be about 3/4 to 1 inch space between the cooling unit and exterior wall. This can be blocked with the use of insulating foam board glued to the structural area around the refer lower vent opening.
Another place to aid cooling is at the top. Make sure that the area above the refer is blocked off so the rising air will go out the top vent. This is really important if the refer is in a slide out.