Hi himanshu in jee mains 2020 there is no criteria of top 20 percentile actually top 20 percentile was related to boards exams sothat either the students get 75 percent or the top 20 percetile to be eligible for applying in joint allocation authority after jee mains but this year due to pandemic josaaa declared that no boards score will be considered as many students were unable to attend their boards classes.

Hope it helps