Like you, I love this plant. I never cut back the foliage because I thought you weren't supposed to do that. I have always used it in the shade too...somewhat dry shade....definitely not wet. This year, I planted three in sun after seeing them thriving in full sun in another garden. The ones in the sun have grown very well and they are in damp soil...where siberian iris thrive and almost do too well. I'll be curious to see how they do in the long run...like over the winter. I always think..."carex...sedge...water", but I'm not sure if they will tolerate really wet areas (of course I haven't tried this). In my yard they seem to last forever, and have been great at lighting up dark areas. I will try to post 2 photos..the new ones in sun and some older (5-7 years) in shade.
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It's borderline hardy for you, so that may explain why it's not thriving as you'd expect. It is fully evergreen in warmer climates and is generally NOT cut back. It prefers some shade but will grow in full sun if moisture issues are correctly addressed. Like most carex species, it likes evenly moist soils and will even tolerate quite damp conditions, especially during the heat of summer, but would prefer good winter drainage conditions. It will not tolerate excessive heat or summer dryness.

Carex is a cool season grass and if you do cut back, it needs to be early enough in the season to allow for regrowth before the heat of summer pushes it to dormancy. OG authorities Darke and Greenlee suggest cutting back to no less that 4-5 inches in late winter if you have to.

Thanks for the feedback. I'm going to move the ones I've got and divide them to get rid of the dead centers. If Darke (assuming Rick Darke) says cut back to 4-5" I will listen - love his books. I was cutting them to about 2" and I just went back to Bluestone's website and they have now amended their care instructions to tease out dead blades as needed in spring. I'm sure that is not what it said before - but that's ok. I got my first plants from them a few yrs ago and have continued to add them around the garden. Its just a great plant.

I grow this carex here in the hot-as-blazes south, but in a lathe house. It does extremely well for me in consistently moist conditions, as was said. Gardengal, when do you divide it? Is there a method other than the usual dig up the clump and slice it? I really love this plant and would like more of it. For my money, the carex family has some of the loveliest foliage plants around!