So I know the program is based around beating a PR in one set, and then pushing past that with rest-pause, but surely some of the training benefit must come from the volume involved in the warm-up sets.

If I feel sufficiently ready to tackle a heavy weight after 3 warm-up sets am I getting less benefit than doing 6 warm-up sets and hitting a slightly lower 6RM? In the second example the total volume would be significantly higher as I'd likely be taking smaller and smaller jumps towards the 6rm and be using decent weight in the last few sets, so even though the 6rm is lower maybe the training effect would be greater.

Correct me if I'm wrong but doesn't 5/3/1 use a number of sets across and then one final all-out set in which you hit a rep pr? I'm sure Wendler emphasizes the importance of the first sets for building muscle.

I get the auto-regulation thing but part of me wishes I had some firmer guidelines so I know I'm not short-changing myself on volume. After my first movements for instance I'm usually quite warm already so on upper-body day the rest of the session after bench is usually just 1-2 warmup sets and one heavy set.

This is enough to get me warm, but is it enough to get me big?

I don't want to overthink this but if I had a rough idea of how much volume was positive it would be really helpful. Cheers.