I was thinking about this as I pulled a pizza out. What causes the difference?
The position of the heating element in an electric oven certainly has a lot to do with it — usually it’s at the top, so something on the top rack will get more radiant heat while something on the bottom rack will be heated primarily by the air in the oven.
Two different forces at work. Depending on which is dominant, the hottest shelf can be either one. One force is radiant heat from the burner; that tends to make the bottom shelf hotter. The other is convection heat from air circulation; that tends to make the top shelf hotter. Doubtless you have noticed by now which is the stronger force in your oven.
Two tips. First, when using both shelves, say, for cookies, rotate the pans about 2/3’s of the way through the cooking time. Second, if (as is more common) you’re having trouble with scorching from the bottom, you can get insulated baking sheets that pretty much eliminate the problem. They also can be placed under other dishes (e.g., a pie plate) to prevent scorthing there.
What kind of oven do you have? Every electric oven I have ever seen has the regular heating element on the bottom and a broiler element on the top. And as someone that tried to bake a cake using the broiler element because the bottom element was broken, it won’t work. Even with the rack on the bottom the top burned and the bottom was still raw.
Interesting; every oven I’ve ever used had the heating elements at the sides, hidden behind perforated metal covers.
Ovens I’ve seen have had an element at the bottom and a gorilla at the top. The gorilla is no good for heating the oven. Our current oven is gas powered.
The gorilla from my oven must have seen a banana and run away, because I don’t have any primates in my oven.
Very interesting. Since I’ve been an adult I’ve had 9 ovens, 8 of them electric, and have never seen this arrangement. Every single one has had an arrangement as mentioned above–a bottom element for baking and a top element for broiling.
Perhaps I’m misremembering — the oven I’m thinking of belongs to my parents, so I can’t check it. (My own is gas, and the element there is indeed at the bottom, with a broiling rack in another compartment below it & the main oven.)
If you don’t have a gorilla, how do you g’ril the cheese on your cheese toasties?
Slight hijack: in my experience, the best way to cook a pizza (assuming you only have a range and not a real brick oven) is to put a baking stone on the very bottom (take the rack out if you have to), then put the pizza in a “crisper pan” and place it on the stone. 450 degrees for about 10 minutes.
Baking stone ? Crisper pan ? I don’t know what these things are … ?
Should we assume from your name that you no longer favor electric ovens? 
IMHO, not a good idea. Depending on the oven, placing a baking stone on the very bottom can (generally will) prevent proper circulation of air from the burner, and the thermostat won’t know about the problem because it’s above the stone. The proper place for a baking stone is on a rack. Whether high, low or middle depends on your oven and whether you’re doing thick or thin crust.
Also, FWIW, I wouldn’t use both a stone and crisper pan, but maybe that’s just personal preference.
Yes, we have no bananas, we have no bananas today.
Which is why my microwave has a baboon.
My oven has “corrugations” on the bottom that allow airflow even with the stone directly on the bottom. If you don’t have corrugations or air channels, yes, it would probably not be a good idea to put the stone directly on the bottom.