Hello Ratatouille,
To have the notes sound even throughout the register, the reality is that we often have to do things differently with our pizzicato (and arco) techniques. The higher up the fingerboard one plays, it is necessary to pull a little harder to have the same impact as lower notes. It feels like a crescendo in the right hand as we ascend, but does not sound that way. When we play arco, we have to move the bow faster in the upper register and pluck harder if pizzicato. We have to play harmonics pretty strong to get them to project.
It is possible that the G string is starting to get old if the harmonics are not speaking. It is possible that a sound post adjustment could also help.
FYI, I have the title of Professor but do not have a Doctorate degree.
Below is a live video of Ron playing with Miles in '64. Notice his left hand technique starting about 5:50 in Wayne's solo when you see Ron playing the G harmonic. He is "tapping" his finger down on the G and his right hand is plucking near the end of the board.
I hope this helps.
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