It's an exacting process.
Take a small white bowl so you can see the individual plants and roots, and cut them into individual plants.
Now take the plants and using a tweezers(pointy is better than flat), grasp two plants in the tweezers and push them into the substrate until all you can see is a little bit of leaf. Pull the tweezers out and the plants SHOULD stay into the substrate.
Now repeat the above and plant a few millimeters away and so forth.
I just work with a string or two of them at a time and cut them all up before doing anything else. The planting process takes a while and you will develop a system.
It can be aggravating to take the time to get them into the tweezers and gently push them in, only to have them float up as you're pulling the tweezers out. Don't be afraid to plant them deep. They will grow out and the odds of them staying down are better if you plant deeply. Also, corys can play hell with your work if not deep enough.
In answer to your question. Yes, they can live and propagate on the surface, but why would you want to do that? If left on the surface for a while they can develop algae on them, as well.
I have a large pad of Riccia that Glosso is growing in. Looks pretty neat growing like that.
Len