I believe you are confused. Admission to Engineering Physics Course at IIT Bombay is through JEE Advanced. In JEE Advanced, unlike JEE Main there is no Percentile System. Being from OBC NCL, you need a OBC NCL Rank anywhere around 1.4k to secure your seat at IITB Engineering Physics or a Corresponding CRL between 7.5-8.5k in JEE Advanced. According to my experience, securing anywhere near 35% Marks in JEE Advanced, in a Moderate to Tough Paper, lands you in Rank Range 7-9k, varying with each year.

As far as IISc Bangalore BS Admission Criteria and Cutoffs are concerned do follow the link below

https://engineering.careers360.com/articles/iisc-bs-admission/amp