Thumbs, mine are set at around the same numbers that Steve Wood quoted above. Like most things in life, the first 95% of anything is easy, that last 5% takes a lot of work.
Your guy was right, my frets are perfect and IF I get it dead straight and too low, you can get that buzz on a few frets.
I've screwed around with this for years now, and I'd offer a few observations from my experience.
For years I played with a HIGH action and heavy picks, just frammed 'em to death. Over time I began to wonder why a bass couldn't play as easily as a really slinky feeling guitar, say like a LP or a Strat.
So I set out after a lower action. I play fingerstyle, a little pick, no slap. Low action will change your playing, as you just can't dig in without a lot of noise, which I hate.
Once you're after very low action, it's important to remember you're dealing in movements of a thousandth of an inch. THIS is the hard 5%. If you're really trying to go very low, very small adjustments can feel WAY big.
All strings are different from set to set and brand to brand. IF you are settled on one particular set, you can steadily refine this. On the other hand, ANY different set (even different guages of the same string, say going from a 45-125 set to a 50-135 set of Nickel XL's for instance) is going to affect the neck differently, as the tension changes. So if you are in that stage we all go through of a different set of strings every time, and your hands can feel the fine differences, expect to do this a lot until you settle on one particular set. BTW, different brands in exactly the same guages will still affect the neck differently, once you're down to hunting a very low action.
I'm always 'behind' the bass, as Alembics take a day or two to finish settling to new adjustments. The strength of the these necks with their laminations topped by a thick ebony fingerboard is a great thing. But you can't adjust it and expect that it's through moving right then. And just like in piloting, your eyes will fool you, and/or most of us don't have the perception to see a difference of a few thousandths of an inch. In other words, I could not do this without feeler guages and rules. I can not tell you how many times it felt perfect right now, only to pick it up tomorrow or the next day and it's just not the same. Pull out the feelers, and then I can see why. You will chase this until you get a sense of your particular bass' wood, how it reacts, how long it takes to settle out completely.
Once you settle on a set and get it like you want, the good news is your hands will 'learn' that feel and it will be much easier to keep that setting and tell if something changes.
There is a deliciously aggravating interplay of neck relief and string height that was not easily grasped by me. I turned my axes into logs any number of times. I'm certain I haven't mastered it. But Alembics are the perfect laboratory to learn this: The adjustable nut, one-piece bridge, the double truss rods, and their enviable build quality allows a lot of experimentation that's easily reversible. Other basses, you'd be unbolting a neck, or adjusting the bridge saddles separately, or cutting or filling a new nut. We get to skip all that.
And it's all very personal. We all play differently, and each bass is different in how low it could go action-wise. I'd easily agree that Alembics probably can adjust for low action easier than most, by design.
There is no right answer or 'factory spec' for setup. I always think the best way is to develop YOUR setup and then measure it. Then, you can always adjust YOUR axe to a particular set of numbes (like Steve mentioned above), the you can ALWAYS get your setup, anytime, anywhere, without having to take it to anybody else.
J o e y