I am unable to edit my last post, so am just replying to part of what I said in that post to make a correction.
I have only ever been able to reproduce the problem where the minimum volume is way too loud when I was using my 200% sink volume boost used primarily during media consumption. When I had the sink volume at its normal level of 100%, the volume has always been perfect during calls. I just wanted to make a correction to what I said, and I suspect the problem I saw was solely caused by me, and may totally different than what the original poster and others are experiencing. Now I just boost the sink volume when needed using the Situations app (which runs a bash script), and drop it back down to normal during phone calls (again with Situations and a script). I posted more information in a follow-up to the link mentioned in my previous post above.