Notification sounds cannot be unlinked from ringtone

So, the OnePlus One has amazing speakers, the best speakers I've had on a phone so far, but unfortunately, the speakers are so loud that the notifications start disturbing the people around me, so I have to turn them down, but that does not work, because I cannot unlink the volume of the notifications from the ringtone volume, so I am FORCED to have the ringtone volume down, so the notifications do not annoy the people around me.... and I DO get a lot of notifications.

I tried everything, but although the settings show that the ringtone volume and notifications volume are unlinked, it still doesn't work.

Someone please help me, I'm tired of having to keep my ringtone volume down just for this...

OnePlus One, stock ROM, 5.1.1 / Cyanogen OS version 12.1-YOG4PAS1N0