Much as I hate to say it, you may be better off with something other than ornamental grass.

The first reason is a grass hedge which meets your height requirements without being "blowsy" is going to almost certainly leave you with several months of dormancy before and regrowth after its annual haircut.

Of the three you mentioned, only Blue Fescue even comes close to your wishes. It's formal looking after it grows back in, but once it blooms, it becomes blowsy. You can trim it back, but then you have to wait for regrowth again.

Any Panicum, and most Little Bluestem will be taller than 2.5 feet, and almost certainly blowsy.

There are some Carex varieties which are semi-evergreen or evergreen, but most of them are blowsy.

I agree with Donn :-) There is nothing in ornamental grasses that lend themselves to a 'formal' hedge structure. First, two of those you suggest are deciduous, requiring cutting back annually, which kinda of defeats the purpose of hedging :-) And as Donn states, with the exception of one or two species (also deciduous), the habit of most OG's is loose and mounding or arching. The only way one would achieve a sense of orderliness with OG's is by very regimented spacing, not by growth habit.

I've seen 'hedges' (or barriers, anyway) created by close plantings of pampas grass, Cortaderia selloana, but they do not look 'formal' or very orderly and they are a PITA to maintain.

I can't say that the idea of a hedge done with this exactly appeals to me but ... I wonder if Helictotrichon sempervirens would do the trick?? It certainly doesn't qualify as blowsy. Question is, would it be happy in zone 7?

Here is a link that might be useful: