Ideally, of course, you'd be baking your pizza on a baking stone, which you would heat to 500F for 1/2 hour before putting the pizza in the oven.
However, you asked about baking a pizza in a metal pan.
In general, you want to get as much radiant heat into the bottom crust as possible in order to make sure the crust is fully cooked and not soggy.
This means that in an oven with a bottom baking element (whether gas or electric)
you want your oven rack in the bottom position.
Again, make sure the oven is thouroughly heated to 500F (250C) (or more, if it'll go higher) before you put the pizza in.
If you have a top-heating oven, things get a bit more complicated.
You'll need to somehow ensure that the bottom of the crust gets cooked, which won't happen if you just put the pizza in the oven, regardless of position.
There's a couple of different ways to take care of this:
Blind-bake the crust until halfway done, flip it, put the toppings on top and finish it,
Do the pizza in a cast-iron pan first on the stove top, finishing in the oven.
In either case, with a top-heating oven, you want to put the rack close to the element ... in the middle or top position, so that the pizza is only about 2-3 inches (5-8cm)
away from the element.
cooking.stackexchange.com/users/7180/FuzzyChef
Serious Eats compared the results of cooking six of the same pizza crusts on different racks of the oven.
The oven was set to 560F, with the heating element on the bottom.
The pizza stone was preheated for 45 mins, and other precautions were taken to make sure that the results were not biased (ie: the stone was taken out of the oven between testings for 30 mins, to allow for temp differences between the different racks).
The results showed that:-Pizza's cooked on the highest rack will have over-cooked toppings-
no good.-Pizza's cooked on the middle rack will have over-cooked bottoms-
no good.-Pizza's cooked on the bottom rack will have burnt bottoms- very bad.
Generally, they concluded that the rack in-between the middle and top (known as the 'upper rack') will produce the best results.
cooking.stackexchange.com/users/18161/mdegges
It depends on your type of oven and your used setting.
Your goal is to have the highest possible temperature to bake your pizza.
cooking.stackexchange.com/users/4580/Mien
Cook pizza on bottom rack, then check half-way before it is done.
If it looks like the pizza crust is very close to being done, but the toppings are not, then move the pizza up a rack or two or more, so the crust will stop cooking and to allow more time for the toppings to finish cooking.
You might even need to reduce your oven temp at this time too.
For an example: If you have it set to 550F, reduce it to 450F until toppings are done.
cooking.stackexchange.com/users/55705/gmn587
Please note the question...
You shouldn't have to be moving your pizza around in the oven or play with the heat!
That's why people are asking this question, so they don't have to do this.
Set oven to highest setting.
Place on top rack and depending on fresh or par baked crust and amount of toppings, see how this works.
At most, you might have to drop the next pizza down to the upper rack.(just below the top rack)
Variables.....
Amount of toppings, thickness of crust, type and style of oven.
In short: Highest heat, start at top and work your way down till your pizza comes out to your liking.
cooking.stackexchange.com/users/55792/Greg
I make pizza in a baking tray in my oven. My question is where do I place my baking tray in the oven, the bottom top or middle?  The resources I have seen so far on the internet are far too ambiguous. For instance,  Yahoo Answers  have given many different answers to the same question.
Pizza in Oven : Bottom/Mid/Top
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<pizza>
cooking.stackexchange.com/questions/24020
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Try using the highest heat and start at or close to the top, and work downwards until the pizza is to your liking.  You should put the pizza as close to the heating element as possible.
In a top-heating oven, put the pizza at the top close to the element. The rack in between the middle and the top is supposed to give the best results.