i have not been able to do the dual range thing with mine,,, the temp fluctuates between cycles enough, and the thermal mass of contents tends to "Share" with its neighbor.
i was able to keep ice cream soft frozen overnite by placing a loose fitting sheet of styrofoam over it in the bottom of the unit. the theory was to let falling cold air in but keep it trapped from exchanging with other contents on top,, worked pretty well keeping the ice cream enjoyable w/o freezing everything else in the fridge.