I have plenty of fighting going on in my all male tank, and fish will hide near the top of at the filter tubing.
Looks like this guy may have tried to get away from an aggressor, and did too good a job of it. I had a 2 inch gap as well, but lost a beautiful Red Top Lwanda. That's when I added that strip. This one was a hybrid, so I'm not overly pissed off, but it's still a bit of a mystery how he got thru there.