Re: Humbucker adjustments
I adjust to suit, depending on what each specific pickup/guitar combination needs.
I don't subscribe to an "always"..."always flat", "always flush", "always radius", etc.
I typically start with a flat/flush position, adjust the overall pickup height to where I get 90% of the response and feel I want, adjust all the poles up, adjust them down to compare and then I fine-tune each string from there, sometimes adjusting the overall height a bit more, as necessary.
Not enough people tweak their pickups this way. They leave the pole pieces flat or put the whole pickup at some predetermined distance from the strings and then complain about undesirable "humps", "scoops" and "spikes" in the response.
You can't completely negate a pickups voicing by tweaking, but you can definitely adjust most pickups to get a reasonably wide range of response characteristics.