Pursuing an MBA as an IPCC student comes with its own benefits. You should consider factors like your long-term goal, professional experience, and financial viability before making a decision. And if you do decide to pursue an MBA you should keep an open mind since circumstances may force you to choose some other college; although there are no logical reasons why someone would go anywhere else if they are getting IIM A what I am trying to say is aim for the best college, aim for 100 percentile and deciding which college to join shall be an easy task for you. As a CA student, you should keep certain points in mind: 

• Know the program: Research and get a thorough understanding of what an MBA is all about and whether your goal aligns with the degree. Familiarize yourself with the curriculum, specialization, and faculty at IIM Ahmedabad. It would also motivate you to put your best foot forward. 
• Strengthen your CV: Although having CA as your qualification is impressive, IIMs usually look for well-rounded candidates with diverse backgrounds. I understand that at this stage you can’t possibly change your background but you can certainly present yourself in the best possible manner. 
• Start preparing ASAP: As a CA student, I understand that you have no difficulty in sitting for hours but CAT doesn’t only test your knowledge but also tests your planning skills and time management, hence start preparing as early as you can. Take as many mocks as possible. 

Yes, there have been mentions of having at least 78% in Engineering for general candidates for admission at IIM Ahmedabad. They may have created the shortlist based on these criteria. The thing is that most of the IIMs want to improve their diversity in the batches as the majority of the students who apply and eventually convert to IIM Ahmedabad are engineering graduates.

So they keep such informal cutoffs to increase diversity. But unfortunately, due to such criteria, many bright students are kept out of the process. Many universities also have toppers who have scored just 65%. But to keep in mind, it is not a mandatory criterion.

One of the top management schools in India, IIM Ahmedabad, selects students into its post-graduate programmes based on a variety of criteria, including academic achievement, professional experience, and extracurricular activities. Although there is no set threshold for the grades needed to graduate, it is recommended to have a consistently strong academic record.

Candidates are often seen as competitive for admission to IIM Ahmedabad if they obtained a grade point average of at least 75% in their undergraduate programme. However, the institute considers the candidate's entire profile, thus a strong performance in the graduation exam alone does not ensure admission. 

CAT, a national-level entrance test for admission to management programmes at IIMs and other B-schools, is also taken into account by IIM Ahmedabad.

First of all, bear in mind that there is never a 100% certainty of getting a call from a specific interest as there are many factors that determine it. 

Considering your profile that lacks work experience and has witnessed a decline in the graduation marks, I don’t consider anything below 99.9 to fetch you a call from institutes like IIM Calcutta, Lucknow, Bangalore, and Ahmedabad. All these institutes only accept the best profiles and high scores. So unless you score a perfect 100, it will be difficult to get admission here.