i think this is how you should scape it:
put moss on the DW - tie it on. then put some sort of taller plant in the back of the DW such as blyxa japonica or pygmy chain sword. in the front plant some HC or something low...idk. maybe just leave the front bare. trust me as long as the front is low, it will look great.
I planned on tying moss to the DW, but as far as low plants go I'm still trying to figure that out. Anymore low plant suggestions? Thanks!