in my experience, the egg crate is way too big and does let jumpers thru, they don't even have to be that small. I lost my favorite fish out of my 135 to jumping thru eggcrate.
Admittedly, this screen does block out some light, but my corals don't seem to mind, in fact, some of them seem to prefer it with the screen on. I've started taking the screen off when I'm around during the day, going with my theory that most jumping happens at night.
But I keep a close eye on it when I have the screen off, cuz I have a Midas Blenny.
It's not hard to find, just look in the window area. You need screen frame, the screen material, or I've heard some people use bridal veil fabric you can find at Joann's, and a little tool for pushing the screen into the frame. All the materials cost less than $15. And it definitely works! I've seen water spots in the screen in the mornings where I think probably the Midas has thumped it. I also read about people using Bird Block netting, which would let more light in, but the holes were way too big for my comfort. I could easily see a fish jumping into it and getting stuck, if not going all the way thru.
I got this idea from hunting and reading threads on RC and other forums.