Buying used almost always lets you inherit a unique set of challenges . . . . if this had been me, I'd have backed off both nuts to where they were loose, left the bass tuned full up to pitch and put it back in the case for a couple days or a week. The neck and your guage strings would have introduced themselves and gotten used to each other. Then I'd have done my setup, fully expecting to fine tune it once about a week later, and that would have been that in most cases.
Sounds like you got to the same destination by a little different route, great!
It's one of life's little mysteries as to exactly how snug each truss rod nut should be: Only the neck relief will tell you. I've decided it's one of those counter-intuitive things: Your head says one thing, but reality shows you something else.
It's once again interesting how much of a fuss theses axes present, coming or going from light to normal strings.
It certainly sounds like you've got this one dialed in VERY well, 1 or 2mm relief is VERY slight, and if it's playing well, you need no more suggestions from any of us !
J o e y
