frige level

Imagine a flat pan with liquid in it. When the pan is level the liquid is the same depth through out the area of the pan. Now if you were heating that liquid it would circulate and mix for a pretty reasonable even distribution of temperature. But tip the pan off level and with the same heat, some of the liquid will get heated and if off level enough, some of the heat can just heat the pan (actually burn it) because it is dry and no liquid to heat in that area. That is pretty much how it works and why if way off level the fridge does not work well and fail far to early. Now for going down the road there is enough movement of the liquid sloshing around that you get even heating and not hot spots on the dry pan.