Fretless sweet spot

[DB]

Hey fretless pros,
I have a fretless Jazz Special, ebony fretboard, black laquer neck.
It sounds great 7-12 fret position, (that Jaco brrr-rr sound naturally) but the rest has no response or life to it.
Can this be cured or is it all technique?
'86 Jazz Special (japan)

 

[Scok]

How much of a curve is in your neck? Try to flatten it out with the truss rod, I heard that helps.

 

[Davidoc]

Make sure you've got some allen wrenches