S7 Edge in-call volume peculiarty

[Stwutter]

I have the S7E. When on a call, if I briefly look at my phone and turn the earpiece vol. down, it never goes all the way. Probably down to what would be the equivalent of about 15% I would say.

Is this normal? It's no biggie, but I regularly speak to people with big gobs, and it's quite pleasant to be able to turn them down to barely audible...