Since eleocharis belem has a curled leaf appearance, it would mix in well with riccia right?
I have belem mixed with my Riccia carpet in the 60-P - you can barely notice it at all. It's only purpose in the 60-P is to help keep the Riccia tied down.
If you want to mix a hair grass that will be noticed with Riccia - then use Eleocharis Acicularis.
Hair Grass + Riccia is a gorgeous combination, and are often found together in the wild.