You mean Sonic Analysis? You can set the ReplayGain preamp volume in the app itself.
However I’d recommend doing the leveling in MP3Gain or Foobar2000 or something. I find the plex analysis is kind of lacking. Thing is, you will never get the loudness perfect because there are a lot of philosophies about mastering.
In programming, everything is just an object in a space. If the devs decided that the object cannot clip and needs some sort of margin, this happens. It’s a decision of design and if the same design philosophy is kept, you’ll always see this.
In some games, you might see a short animation of someone getting into a bed, during which you can’t move. After that, the objects bed and player will be fused, as if they form one object. Maybe the game is better suited for meeting them separate, who knows. Considering the large number of different objects, you might be surprised how it is possible players aren’t clipping through everything.