If your numbers are both near or below the 25% line of a school, you are not getting in. Unless you are a URM or have exceptional life experiences like living in 5 different countries, being blind, speaking 5 languages, starting a non-proft, etc. The reason 25% of a class gets into school X with below a 3.4 gpa is because those students probably scored in that school's 90% on their LSAT, pulling up their index number. Or they benefitted from Affirmative Action in some way.
Likewise, someone with below a school's 25% LSAT probably had above that school's 90% gpa. It is sort of a sliding scale, wieghted towards the LSAT at most schools. If your numbers are both over a school's 75%, you are in, except at some of the Ivies or if you wrote your PS in crayon. Even in either of those cases, you still probably get in.
If your numbers are somewhere between being an auto-decline and being an auto-admit, they will look at your LOR, PS, resume, etc, and admit you if they feel that those components of your packet are strong enough. Like it or not, numbers drive this process. This is not med school admissions, numbers are exceedingly important, for better worse, in LS admissions.