Heating element on electric oven

it involves thermodynamics.

The simple answer is install the heating element on the bottom.

The complicated explanation....

In baking, the heat transfer involves three factors:
1. heat source (in this case, the heating element);
2. transfer medium (in an oven, it's the air and the pan/baking surface)
3. the food itself

Temperature and heat are two distinct features. Heat increases/decreases temperature, but in baking/cooking, the temperature we select is the driving force of heat.
* Temperature is the force that moves heat.
* Heat moves from hotter materials to colder materials.
* Higher temperatures forces more heat to transfer from hotter material to colder material

In an conventional oven, most of the heat transfer happens through conduction, meaning it's a transfer of energy molecules through the air and pan/baking surface into the food.

The air is important. The difference in weight between the molecules determine how the air is heated. Hotter molecules are lighter and buoyant, so rise. Cooler molecules are heavier and denser, so they don't rise. If the heating coil is on top, the hottest molecules will be concentrates at the top of the oven; they won't disperse downward. If the coil is on the bottom, the buoyant hotter molecules will disperse upward and outward, more evenly heating the entire oven.

I say more evenly since it's impossible to achieve uniform heating in an oven. As the walls of the oven heat, they will also radiate heat from all sides. When you place a pan, stone, or baking steel in the oven, the heat flow is disrupted by the mass, redirecting the heat in every direction.

Ok, so that's the complicated answer to your question about where to place the heating coil.

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The uneven browning of your bread is mostly likely due to a combination of temperature, rack placement, type of pan/baking surface, and humidity.

Temperature: preheat oven for at least 30 minutes before baking. Check the oven temperature with an oven thermometer. Place the thermometer in the center of the rack you will bake on. The temperature will vary throughout the oven due to heat transfer. So you need to get a reading in the spot you will actually use to bake. Also, all ovens have hot spots. If you bake in a hot spot, you'll get uneven browning.

Rack placement: it's not just the temperature that you select, but where you place the rack that determines the temperature you will bake at. Since heat rises, there will be three different temperature zones in the oven: intense heat at the coil; moderate heat in the center of the oven; a hotter zone at the top of the oven due to dispersement of buoyant molecule. Check the temperature at the top, middle, and lower rack positions to find the zone that is the correct temperature.

Pan/baking surface: heat transfer happens through the pan/baking surface. The efficiency of that heat transfers depends on the material. You have to understand a little bit about the baking surface materials you are using. The materials you use determines temperature.

Humidity: moisture slows the baking process by absorbing some of the heat. If you are spritzing the tops of your loaves or adding a steam source in the oven, you are delaying that baking process. Which is good for crumb and crust development. You just need to make sure other factors aren't increasing the baking process under the loaf (e.g., rack placement, temperature, hotspots, baking surface).

One last thought...there's a trick that pastry bakers use to prevent burnt bottom syndrome.   It's called double panning.  I've never used it on bread, so I don't know if works on bread.  But cookies, rich doughs like croissants, you can prevent burnt bottoms by placing a second baking sheet under the pan.

at the same time to preheat and bake.  If you find the top browning too fast change to just bottom heat for a while or place a foil tent over the loaf to protect it from burning.  Small oven?