So how can one find out or research what school/s had/ have a bigger grab from BA?
This idea is somewhat self-defeating. You'll be up against the best candidates if you progress far enough anyway. If you're not good enough to get to the final day from a single school, you're not likely to make it through the final day should you have gotten there via an alternative route.
Your time would be far better spent trying to make yourself the best possible candidate you can be. Forget about the odds of x, y, z - it's all high pi in the sky.