Why does a smaller amount of propanol burn slower than a much larger amount?
For "burning" you need oxygen because actually when a compound is burning it's what is called an oxidation following this reaction  

$$\ce{C3H7OH + 5O2 -&gt; 3CO2 + 4H2O}$$

with propanol called the combustible and oxygen is called the comburant. Both are required as well as a power source to start the combustion process.

So in a plate you have the air surrounding the compound then you have practically an endless amount of oxygen available. 

So the reaction will stop when all the Propanol will be consumed. 

Hence, in a jug, this time the limiting reactive is the oxygen because you have less oxygen supply. Then the combustion will stop when all the oxygen will be consumed in the jug.  

So, to sum up, in the jug the oxygen will be consumed faster than the propanol in the plate, that's why the combustion last longer in the plate even if you have more combustible.