When it comes to the +0.1 dB boost, I'm mostly talking about the pre-mastered version, as I mentioned the difference depends on what the signal level is to begin with, which is the whole point. If you cannot notice this difference, you either are used to much more dynamic content or it's something else, such as you haven't paid enough attention, you monitor on much lower volume or your monitor/converter solution does not reveil it in the same way as in my case. I have a very high end monitoring chain and I'm always amazed at what as little as a +0.1 dB boost can do to the mix. The master bus gain staging is one of the more important things I do in mastering, simply due to this very reason. It's about finding that -0.1dB below audible clipping, just much enough to use the full capacity and just little enough to leave the transients nice and clean. It can be tricky, but when you truly find it, that's when it gets sweet!