Hi Jenn,
Your question is a bit of an odd one--schools typically do not have "minimum" requirements of anything, even LSAT scores (which is why, ever year, students with relatively low LSAT scores get into the most prestigious law schools--other things in their applications allowed them to stand out enough to be offered admission). When you say "index," I assume you mean the result of the index formula which some schools use for admission and others don't. However, those formulas (which are customized for each school) are not publicized, so I'm not sure where you could be getting them and plugging in your numbers.
In any case, here is my advice:
1. Become familiar with the LSAT/GPA ranges each school prefers (again, these are not "minimum" or "maximum" numbers, but ranges in which the schools accept the majority of students). You can find these in LSAC's Official Guide to Law School Admissions, here:
http://officialguide.lsac.org.
2. Aim to obtain an LSAT score well within or above the range for the schools in which you are interested. This will allow you to maximize that part of your profile.
3. If your GPA is well below what a school looks for, aim to get an LSAT score that is well above the 75th percentile of what the school typically prefers. This will minimize the damage done by your GPA.
4. Don't worry about "indexes." Instead, focus on presenting the very best application you can, from your letters of recommendation and essays, to your LSAT score.
If you put forth a strong application, with strong numbers and a cohesive essays and letters, you will be considered for admission, regardless of what any index might say.
Best of luck!