I used to keep my plexi glass under my screen top but what happened was that my snake managed to squeeze in between the screen and plexiglass and ended up rubbing some scales of his head and causing a small wound. Thats why I opted for keeping the plexiglass above the screen.
That's interesting. I am gonna start building a new set up soon so I can get rid of those stupid screen tops. but until then I will keep an eye on my snakes so they don't hurt themselves. Thanks for sharing your experience