I have bumped it to 12db and I don't see any effect it has on clip volume or track volume.
Large volume adjustment is for clips, not for tracks. The maximum positive adjustment is +6db. So when you set up the large adjustment to 12db it could be possible that nothing happens.
If you want to increase the clip volume more than 6db, you can use the audio gain option. Right click on the clip and choose audio gain.