My knowladge of viviapar is limitted, but heres what i do know. Its quite possible you have it, put wait to see once its established first. What happens is the grass leaves will reach up, then they will get a bud like growth on them. From there another plantlet will grow. It can be a very messy plant is kept untamed. The idea is,if you like the matted look then let it grow, just like in the huge Iwagumi tank Amano has with 1000 cardinals in it. Or you will have to nip the plantlets off as the grass grows. Which im sure is very time consuming. Othere wise, if its just hight your after, then E-acicularus will do you fine.
Cheers.