A question about Proficiency gain

So, I understand the base rules for how Proficiencies work, but I’m curious about the value/gain in proficiency progress.

Is it only time taken? Does skill requirement come into it? Do the materials involved count? What is the sweet spot to aim for to get a Proficiency most efficiently?

Time taken (and some recipes can make recipes learn more or less for the time taken, but that’s quite rare).

are there any lists of recipes that give more per time?

No list exists, because no recipes of the like exist, only ones decreasing it.

oh, so I guess that’s why lockpicking prof on my old char doesn’t increase - she’s too good at the job so she’s picking locks so fast, time spent doing that is not enough for the proficiency to get even 0.1%.