Go out to a local library or good bookstore and take a look at a good book on ornamental grasses. There you will find all sorts of pictures and descriptions of what conditions they will take and what size they will attain etc. The web is also good if you visit a good nursery's website and look at pictures of different grasses and read what they like.

If your in Texas and your planting in a "hell strip" (new term for me) will you be giving them regular water their first season and semi-regular in the hottest periods thereafter? Miscanthus sinensis 'Arabesque' may get both taller and wider than 3x3 -- more like 4x4 perhaps. Miscanthus sinensis 'Graziella' will be about 3' wide but more like 6 feet tall in flower. Miscanthus sinensis 'Adagio' is about 3-4' tall and perhaps 3-4' wide. Miscanthus like full sun, but Texas sun can be altogether different from what I recall. You could coonside a native grass planting with rocks and small drought tolerant shrubs. Check what's native to your hot open grounds.

There is a grass called Muhlenbergia capillaris. It is close to the size you want and can handle harsh conditions. Very drought and heat tolerant.

dereks suggestion is a good one!