I think I might understand this one. It's very easy to get into the habit of mixing by reduction. You hear the mix, and the bass pops out, so you pull the fader a bit - then that trumpet bursts out at the chorus, so that comes down a bit revealing an over loud piano, and so on - eventually you get the mix just right but discover you are just tickling the master meter - the peaks maybe half way up. I have no idea what level I master to, because I never adjust the monitor volume. What I hear from the speakers has been mixed at what my ears like. For me, invariably it will be a bit too much, so I listen and think this is just too loud for the balance I want, so I pull the master fader down a bit. Occasionally, cubase shows me the red lights, and I know I over cooked it somewhere, but I never mix with master levels visible, I have them off the screen, so I'm doing it totally blind. I can easily fix the average level later, and for me, it comes down usually. I guess here, the OP has mixed too low, so has to boost the master, and that'w where these dB mentions come from. I suppose you could go through track by track and nudge them all a bit, but that might alter the way effects and processors sound, so as long as you don;t hear noise or distortion, then I see nothing wrong with pushing the output fader, or even just normalising the file if the noise is evidently way down and not an issue. I have my own favourite normalistion settings for loud, medium and quiet tracks. The loudest, busiest, angriest tracks would perhaps be -3dB below maximum, but a quiet track could sit normalised at -10dB if that weas suitable. As for LUFs, no idea, I refuse to play the numbers game, and Spotify and youtube seem to work just fine. I am, of course, simply wierd!