The Signia also don’t connect well in large open spaces (walking the dog up the hill), but my early Phonak had the same issue. I had to move either my watch or phone to my chest pocket for one section of the walk.
So for better reception, I would suggest as clear and short line of sight between your device and hearing aids. Also hard reflective surfaces seem to help (walls) if they are not between you and the source.
This was a common problem with running watches (Garmin, Fitbits etc) connecting to Bluetooth earbuds. Outside Bluetooth does not have the reflective surfaces (as you say walls etc) to bounce the Bluetooth signals from the watch to the earbuds and so there were many forums where people checked which side primary earbud Bluetooth receiver was on so you could match that to which wrist you wear the watch.
Modern Bluetooth (5.3 - I think - and onwards) + True Wireless Stereo (TWS) earbuds address this so both earbuds can connect directly with the phone/watch and with better range.
I have no idea whether hearing aids are using TWS and Bluetooth 5.3+? Hopefully they are?
My Airpods Pro 2’s (with hearing asistance) connect seamlessly with multiple Apple (and non Apple devices eg Garmin watches) and switch to the one I am using.
My hearing aids (Eargo 7’s) don’t have Bluetooth - which is fine for their form factor. For life, video calls, phone calls (I can use the phone/computer/car speakers and mics) etc I don’t need it.
When I do need Bluetooth for streaming / hands-free I will use the Airpods Pro 2’s
It does seem from comments here there are many more problems than there should be with the Bluetooth connections between hearing aids and phones. My iPhone 11 Pro (not the latest Bluetooth), iPad, Garmin watch all have no issues with multiple TWS earbuds.
You’re ignoring this member’s posts.