Liriope comes in two types - clumping and spreading. Liriope spicata is the spreading type and Liriope muscari is the clumping type. Note - clumping grasses or grass-like plants DO increase in size with time.....they just do not expand with vigor or uncontrollably like the spreading or running types do.

In addition to the hakone grass, I'd consider some of the Japanese sedges - Carex morrowii or Carex oshimensis. Most are well-behaved clumpers, although Carex morrowii 'Ice Dance' does expand rather vigorously for this species.

Ahh i did not know that about the liriope. I'll look up the Carex, never heard of that before.