@jeffpa, IIRC, the more open the fit, the more poorly Spheric noise reduction works because there is much more sound bypassing your hearing aid processing and going directly to your ear drums. Much more important for someone like me with decent low-frequency hearing, so I plan to wear an occlusive fit.
For whatever MS Copilot info is worth, it says the following about the turn-on threshold for Spheric noise reduction: Phonak AutoSense 6.0 is 65 decibels (dB) for a duration of 5 to 10 seconds . Since I have a good decibel meter app for my iPhone, I’ll put it to the test when I get my Spheres.
As to adjusting the sensitivity threshold, here are some screen captures from Target. Others may have posted similar already in other threads but here it is again.
