Line-in volume

I'm running Linux Mint 20.2 (x64 / Cinnamon).

I'd like to play sound from a device connected to my sound card's
line-in. I'm able to do so by enabling the loopback device in
alsamixer. But even with the line-in level and line-in booster level
set to 0, the volume is too loud.

Adjusting the line-in volume level in pavucontrol seems to have no effect.

Is there a way to reduce the volume level to an acceptable level?

-- Paul