That will be problematic..
Riccia Fluitans is actualy a floater, i tonly sinks to the bottom during dormancy (winter time in cold climates).
In a way you can compare it's propagation a bit like duckweed, it just splits in 2 and grows on. Tho, it's a crystalwort (liverwort moss) and it does grow hair roots (rhizoids) but these are very fragile.. Best example to understand is looking at this microscopic cross section of a Riccia sp.
Those tiny short filaments at it's underside are the rhizoids, it is so fragile that when growing Riccia submersed its own buoyancy can rip it off any surface it attached too. Actualy its not even natural for Riccia to attach submersed, it rather likes muddy riverbanks.
Or uses other vegitation to grow into with clumps.
So, it thus formes clumps, because it grows like a fork and intertwines its leaves with eachother and also can attach to eacother with it's rhizomes.
Looking at bellow picture is the best example to see how it grows into eachother.
Now thats why best practice to attach it is to take such a clump and tie it to a piece of wood or rock. When it grows on it will hook into eachother till it grows in such a size that is bouancy will break it apart.. When using mesh than this is the best way to use it.
This is also how the finer maze stainles steel mesh in the lfs is propagated, put some mesh on top of some ricia and wait for it to grow through and over it.. If the mesh size is to small it likely wont easily grow through. No glue needed.