Fretless setup - strings parallel to fretboard?

[Quicksilver44]

I have been in a battle with my Squier fretless jazz bass for a few months now.. I'll start by saying I love the bass but what I really want is the lowest possible action without buzzing. Heard it a million times, I know... But I have a specific question which I haven't been able to find on the forum..

Also, I'm no stranger to basic setup adjustment to the bass.. But the problem is I don't know what makes a perfect fretless setup for what I want.

I've shimmed the neck, I've tried the neck completely straight and slightly bowed, I've adjusted the bridge saddles and all combinations of those things and what I've found is that no matter how low I can get the action at one end of the neck, there's buzzing at the other end. (or where I'm fretting, of course)

Basically I want the action to be consistent all along the fretboard. Looking down the neck, I can see that the strings are naturally higher at the 12 - 20 fret positions because the neck is not parallel to the strings. Am I crazy or doesn't it make sense that the strings being parallel to the fretboard would yield the best possible action? Shimming the neck doesn't seem to solve that. The only other thing I could think to do is to raise the nut slightly. OR does the neck NEED to be slightly offset from the straightness of the strings?

Hopefully someone can help me out here.. I'm completely losing my mind!