Salvia blepharophylla sounds ideal for your spot. Make sure the soil is humusy and can hold moisture, though. S. miniata might work, but it gets taller. This puts it in the same class as S. elegans (pineapple s.) and S. coccinea (tropical s.) Also, consider S. chiapensis.

S. roemeriana (cedar brake s.) will grow in full sun. I saw it on a visit to the San Antonio Botanic Garden when Paul Cox was there. The plant was quite dense with bloom. One disadvantage is that the flowers become cleistogamous in hot weather, self-pollinating while they are just about to emerge from the calyx.

Salvia greggi 'Furman's Red' has grown sun and shade for me, prolific bloomer. For me, it looks a bit greener and lusher in shade than in sun.

I live just a little north of Austin and reall enjoy my salvia Regla. It might get a little wider than the 2x2 area and will get to about 4 or 5 ft tall but it does very well in dappled light at my house. The only draw back I have is that it doesn't bloom untill late Sept. but when it blooms it puts on an amazing show for several weeks. As a matter of fact, mine were still blooming when the big freeze hit in December. They're dormant now but I can't wait till next fall.