I only use glass on the back of my big tank that has a canopy.Tha back 6=8 inches or so.
The fish could have only jumped out in the back ,otherwise the canopy acts like a 'backboard' in basketball and they just 'rebound' back into the tank [I assume] ? I have not lost a fish in years.
Many buy tanks at the $ per gallon sale [Petco] and harvest the glass for cheaper then most tops,with thicker glass to boot.