How exactly does focus affect learning?

I’ve been scanning through the game’s source code to try and get an exact idea of how focus affects learning from hands-on experience, but I can’t really seem to find anything beyond it helping the player block more during combat. I know focus plays a role in calculating skill gain, the difference between 10 focus and 100 is staggering, but I can’t find the exact code for it.
Based on in-game testing I am vaguely certain that at 200 focus you learn twice as fast, and at 50 focus you learn half as fast, etc, etc? Kevin can you confirm my suspicion, or if not, just show the exact calculation(s) for how focus affects skill gain?

100 is 100%
50 is 50% etc.

However this only applies for one “tick” of learning.

Fast/slow learner add/subtract a small value (I think 15) from focus used in calculations.

The effect is of marginal value, really. Base focus is…unremarkable. Does make it hard to just binge learn stuff, which is ok, but I’ve never run out of focus before, and I’ve never seen the appeal of buffs to your focus. I guess it’s never been plausible, or necessary.

It needs some modifiers. Something like ADHD or something; double regen up to 100% but double the decrease. Or something of the like. Maybe something that makes it so that you lose it slowly on things, but it also goes up just as slowly. That’d make it more interesting.

We must have very different experiences. I find higher focus to be very important for skills past level 6; without at least a constant 125 focus, it becomes unbearably tedious to level up otherwise. Of course, this is only for combat skills, which can’t just easily be brought up to high levels by reading.