it takes some trial and error. I have my frig side set to 36-39F, which is measured at the back along the wall and it probably is at a "warm" spot, but is running about a 50% cycle time. Things on the bottom would freeze till I added a fan and changed the main fan to run all the time. I have my freezer
set to 11-16F and it is measured at top of plate about 1cm inside, so that again is at the top of the box. I found setting lower used a LOT more power and even at this setting the food
in the mid to bottom of the box was rock solid.
FYI I originally had a spillover system, which is just a freezer with a passage
between it and the frig with a fan. Last year I added a small frig unit and sealed the holes. Am getting a LOT better cool performance now at the same power use that the single
spillover system did