The banding should be for the job not the individual,thats right.
The overriding thing that affects what band your post is given is who sits on the evaluation banding panel and how awkward they want to be.
We had lots of trouble and eventually the whole department went to full JAQ. Even then we heard from a wall that had ears that a SNM who sat on a panel argued that we didnt do core things within our function.
Best bit of advice I got was find a bod thats sat on job evaluation panels and is friendly to you request and knows a bit about what you do. Then let them pick your JAQ to pieces before you give it in.
And dont underestimate the power of descriptive wording, panels have long list of what a word means e.g difference between manage and organise. They will take you very literally in what you put down on paper.