Hello Mayur

You have asked very good question.

If no of students decreased in April attempt thenn your rank will decreased.

Suppose 

In January attempt you get 90 percentile and total number of students  is 874469 and from that you got approx rank 87664 approx.

If In April attempt you get 90 percentile and total number of students reduced to 800000 and from that you will get a approx rank 80000 approx.

As you can see their is difernce between 2 ranks it will help you to find more good gollege.

I hope you get my point.

Good Luck!!!