When making fried rice, how does the amount of heat affect the taste of the food?
It's an issue of thermodynamics.

When you're cooking food, the food cools itself off through evaporative cooling and the energy being used to cause chemical changes in the food (eg, caramelizing sugars).

If you have too much food in the pan, the balance is overwhelmed by evaporative cooling, and thus you can only get to the boiling point of water.

To change the equation, you need to do one of the following:


Use a more powerful heat source.
Cook less food at a time
Reduce the amount of moisture in the food before cooking it.


You'll often see advice for #3 -- such as patting dry steak or chicken before grilling it, as without it, you won't get good browning.

You can't do that when you're dealing with sauces.  You can try cooking less, but with sauces you cause more problems -- if the pan size is the same, the area for evaporation is the same, so you don't really improve the balance.

With a sufficiently sized burner, you can actually heat sauces above the boiling point, as you're putting in energy faster than evaporation can cool it.  This which will change the chemical reactions that occur, thus the resulting chemical compounds and the resulting flavor of the food.