According to the circular released by the National Testing Agency or the NTA during the press release it was told that 6.97 lakh students appeared for JEE Main, which is quite less as compared to the previous years. The effect on the percentile can be understood as follows:

suppose you scored 99 percentile last year (8 lakh appeared), then your rank would be 8,000.

However, if you score 99 percentile this year, your rank will be 6,970. So, for the same percentile your rank will become better.

Hope I have answered your question. All the best!