Enquiry - Pleioblastus pygmaeus:
I've never had this plant get over 12" to 18" and that is usually only if it is grown in deep shade. In full sun it tends to stay shorter, more compact and dense. You can also cut or trim this bamboo ground cover with a mower or weed eater periodically and it cause it to flush out with new growth.

It is a running or spreading ground cover, spreading by an underground rhizome system (like a grass, which it is) and not by seed or above ground trailing type stolons. It is very easy to work with and control.