sorry, forgot to answer that.....the plexi is cut so precise, that once it goes in, past the leather in the corners, it "bites" itself into place. It has nothing but the fact its snug, and the corners "snag" just right. Its hard to explain. It is upside down 99.9999% of the time and so far, it doesn't budge. Plus, my little pick-tool can get behind it and pop it out with a little pull in a few spots. It actually does not fall out but is easy to pop out if you need to. Win!
what about the bass pressure would that make the glass rattle out