Delphi - I think you are right that it's probably pointless trying to finesse when numbers are so small. At that level, it's probably more about the personality / fit of the interviewers on the day and the strength of individual applications overall.
It was a broader point really that colleges are (rightly) aiming to achieve a certain balance in terms of the independent / state sectors. Having said this, they also claim to contextualise selective grammars in the same way as equally selective independents. For instance, Kings College enjoys a reputation as being a college with one if the highest state school intakes, yet DC and friends say they are yet to meet one who wasn't at a grammar or selective academy.
But in very broad terms, a college that still only receives 60% of its applications from the state sector, may be more likely to go to the pool to seek a more balanced cohort because they are all aiming for a certain target (maybe 75-80%) which has to be published.
Apart from this, the stats across subjects and colleges suggest some tutors seem to take from the pool every year, whereas others never do. Whether this is their personal preference, or whether they always receive less / more competitive candidates is impossible to say.
Its probably a good idea to choose a college that takes a consistent number each year. For instance, when we looked at the stats for the subject mine is studying, there was one college that takes only one or two each year. That year, they had ten direct applicants but took none of them - nobody was pooled and they took nobody from the pool. It's hard to believe that not one if those candidates was worthy of a place and you have to wonder if they just decided not to bother with the course at that college that year, but didn't really push their candidates to colleagues elsewhere.
It's different at Oxford because they seem to make decisions on a departmental level and they will redistribute students from oversubscribed colleges to those with less applicants.