Seems I have to give up, the Ehrlund PU doesn’t works on my new bass.....

It has been mentioned before - in addition to placement, the distance from the top, and amount of putty, is critical. On my bass, it is very close to the top, < 1 mm. Keep trying; as you know, it can be worth it! Mine hasn’t moved location in a few years now...

 

Usually, yes - because the output and tonal response can improve, and that minimizes the need for preamp gain increases and radical corrective EQ, which can both be sources of problematic feedback.