Good Morning

In the JEE Main and Advanced , the minimum requirement of top 20 percentile means that you are in the top 20 percent of the respective board. In simple language , some boards have very strict marking criteria . So, the top 20 percentile cutoff will be far below 75%  like  for Odisha board in 2017 it was 331 marks out of 500.

Hope you found the answer useful.

All the best