If I understand you correctly this is how I was thinking of doing mine on my new set up. It would gain a little space as the crate would be longer front to back at an angle than it would be front to back laying flat. Like this _ compared to /
My concerns are A: the frags falling out or pulled out easily by crabs, snails, fish. B: Cleaning under it.
I think I could get around the cleaning under it by using some framing and making a square access hole in the middle to temporarily remove the middle section of rack. I probably would just not angle it a whole lot to avoid frags being jostled around. Obviously the greater the angle the more space gained, but the easier to uproot frags as well.
like this...
Yes this is the design I was talking about.