Ultimately the water changes is key to cleaning up after monster appetites like Rays and Bass. The filter is just a tool to postpone a water change.
Of course the larger the sump you can get the better. More water volume in your system will allow you to postpone a water change that much longer.
The key to sumps or any filter is ease of maintenance. Make it easy to change your mechanical filtration. Look into filter socks, they are easy to change but pricy and a pain to clean and reuse.
At one point I had a 5 gallon bucket with holes drilled in the bottom that I used as a pre-filter. I filled the bucket with filter floss stuff I bought in bulk and I would just change out the bucket every couple days with another bucket filled with new filter stuff and dump the dirty filter media in the trash. It took less than 5 min, really it only took 2 minutes. Down side it was loud and took up a lot of room behind the tank, but my old house the tank was built in the wall and the filter room held in all the noise.
Anyway, make the sump large and easy to work on and make water changes as easy as possible.