Calamagrostis 'Karl Foerster' is a great grass for zone 6 and would be a perennial grass for you, rather than the tender perennial, Pennisetum 'Rubrum' (purple fountain grass).

It would fit the height you want perfectly, doesn't self seed at all, and maintains a very controlled manageable clump. These are all reasons that made it a perennial plant of the year selection. They are a very erect, formal looking grass, but soft enough in plume to fit the casual garden. Works great as specimens or backdrops.

BTW, I never have much trouble with Pennisetum 'Rubrum' flopping if grown in full sun. It also grows out so quickly, that if weather makes it ratty in spring/summer, cut it back and let it flush out again.

Just cut my Rubrum and other grasses back this weekend. I'm waiting on the Rubrum before I replace, to see if it'll come through. I'm right on the edge of hardiness and it's almost a coin toss here winter to winter.

As usual all my questions answered. Thanks grass guy I am going to plant 3 or 4 karl foresters in the spring.I appreciate your expert advice and this wonderful forum.jjbjr