I'm not so far into the game, but I am not gaining any disposition at all and the "list" beneath the book on the right is completely empty. I have chosen a variety of options, diplomatic, aggressive, etc. but nothing is showing.

I definitely told the pirate at the start that I'll take his head, which is given as a textbook example of aggressive, yet the disposition list is completely empty.

Use this console command to check:

ToggleDispositionDebug

Each rank should breakdown as:

1. 4 points.
2. 12 points.
3. 25 points.
4. 45 points.

Right, so it shows absolutely nothing until I hit a certain threshold, in contrast with the companion stuff that shows every entry...inconsistent design, but thank you for the answer.

Yup only Companion relationship ever show a breakdown of the different axis changes.