Hello Greetings 

Percentile Scores are calculated in Your Respective Shifts, The reason Being mention By JEE Main which is

"The candidates will be given different sets of questions per session and it is quite possible that in spite of all efforts of maintaining equivalence among various question papers, the difficulty level of these question papers administered in different sessions may not be exactly the same. Some of the candidates may end up attempting a relatively tougher set of questions when compared to other sets. The candidates who attempt the comparatively tougher examination are likely to get lower marks as compared to those who attempt the easier one. In order to overcome such a situation,“Normalization procedure based on Percentile Score” will be used for ensuring that candidates are neither benefitted nor disadvantaged due to the difficulty level of the examination"

Hope this Helps All the Best