
This is the connection setup I (used to) see with my older GN ReSound LiNX Quattro hearing aids.
Note that BOTH Control of the hearing Aids AND Sounds sourced by the iPhone such as call audio, and Streaming audio are sent over a Bluetooth LE connection directly to my hearing aids.
All audio sourced from the iPhone is subjected to your hearing 'personalization' (that Graphic equalizer) in the Hearing Aids, then presented directly into your ears.
I stream a local radio station's web stream (using their App) directly. It is mostly talking with some music. I have not observed distortion or drop outs under MOST conditions, but there are a few cases that do not work well.
When making coffee with the microwave oven heating the water, there is a lot of interference. This abates immediately when the microwave shuts off. This is not surprising, since Bluetooth shares the 2.4 GHz band with Wi-Fi, and microwave ovens are know noise-maker in that band.
When I place the phone in my SHIRT pocket, I get good strong interference-free reception of the Audio stream. In my back trousers pocket, the Bluetooth radio waves do not go through my body very well, and sometimes one or the other hearing Aid drops out when walking outdoors. When I experience this, I just move the iPhone to my shirt pocket and all is well.
I have not experienced distortion or tinny sounds, but maybe we can help each other think about why that might be happening.