Is it true bio-balls lose efficiency if completely submeged in sump filter?

I heard someone said so, and you should be letting it be floating or always be on the top of other medias, so it helps with the biological filtration better than having it totally sinked in.. I ask this because I finally decided to clean sump filter that works with my 250 gallon. I haven't cleaned the sump in a quite a while. And I also added new media to help with the bio-load, and I decided to just let the bio balls be at the bottom, while the medias like "eheim substratepro", "fluval ceramic rings", on top, and scrubbies on the center. Should I swap the rocky hard porous media to the bottom and bio balls to the top?

What do you guys think?

Thanks.

Thanks guys. Just did the swap and the bio balls are on top now. I know I'm gonna have a huge bio-load in the future after my young monsters become big foot giants. So I'm glad I'd outta be ready.. Appreciate it folks. See you all around MFK.