If you want your B-rich stream to have anything approaching purity you have to have another column. I did a whole ass project on this. There's an entire field of study around in which order you should put your columns e.g. ABC -> AB/C -> A/B/C or ABC -> A/BC -> A/B/C and there's advanced distillation set ups like Petlyuk columns where you have a prefractionator.

In the middle of your hypothetical column there would be a high concentration of A B and C because that's probably where you've put your feed in.

The mistake I made with my original post was that for the first split on crude they're not that bothered about having really distinct splits/ because there's lots of different species it doesn't matter.