M. reverchonii is, I think, a warm season grass. If you cut it back now, it's probably close to done until next spring. From what I've read, it likes a lot of lime in it's soil. Is it possible your soil is too acid for it's tastes?

I have 2 that came up volunteer that are about the size yours are this year and have that same upright appearance (upright now anyway). I'd mistaken the identity thinking they were Indian Rice Grass where I'd sown seeds. I'd leave them where they are because they have nice late afternoon sun nicely showing off the pink but....they get so large they will be too big for the spots so I am moving them next spring while they are still a moveable size (gallon sized). Too bad because currently they look great and I wish they'd stay that size. A mature plant gets 3 feet, forming a very thick, dense tussock that forms a perfect half circle shape (no longer the upright look) that is just as tall & really takes up a big space, its more like a specimen grass which I hadn't expected. They are a bear to trim down in spring. I took one out this spring to open up some space and in its spot there are now 6 bluestem plants with room to spare. I had no idea they got that big. Peren.all, you would probably be able to grow Muhlenbergia riverchonii, its often sold under the name 'Undaunted'. Its a lot more cold hardy and personally I like it better. Even if you could grow the Gulf Muhly you might never get the blooms because the Gulf M. blooms so late in the season, my big guy is just now starting to put up a only few blooms even though the two volunteers bloomed earlier and are in full bloom. The M. riverchonni starts to open in July and is in full glory by mid August, then it looses the color but stays nice and hazy looking until its cut back in late winter. It is more subtle in color---kind of a dusky pinkish purple color + its a smaller, lower growing grass with leaves that are just as fine but more grayish green. I think the Gulf M. looks more 'tropical' because its so garishly pink with brighter green leaves.

Lindheimerri Muhly does very well for me, even in difficult spots of dry clay & it tolerates quite a bit of shade up here in OKC. I grow them in dry spots because otherwise they get too huge. Mine look really good growing in an area infested with tree roots on the high end of my property but I did give them a good soak twice this summer. Switchgrass on the other hand needs quite a bit more water and looks better with more sun, it tends to be stunted with lots of browning leaves in in dry years and doesn't color up here like it does in other parts of the country where summers are less intense, mine usually just turns from green to brown. I've never seen any red on the varieties that are supposed to turn red. I read the same thing happens to the guy on the Plano Texas Prairie blog, his tend to just go brown in fall. Switchgrass likes water. The best looking is 'Northwind' & I ordered several more to do a mass planting. My 'Heavy Metal' ones didn't do as well and are terribly dry looking but tall. Big Bluestem needs a lot more water than L. Muhly to grow good, at least the younger plants do, otherwise they get lots of brown leaves in summer. I have them planted with 'Northwind' switchgrass in my lowest spot where its easy to soak and where the water drains down when it rains. I watered them when it was very dry. The single "Red October' Big Bluestem I have growing on the hot, full sun, dry hell strip will be moved come spring (poor thing). I've got some very tall types of Little Bluestem that do great there and which are almost as tall as me but Big Blue suffered badly this year. In a friendlier spot, those Little BS would flop but as it is, they are are tall, straight and a deep rich mahogany color after being gorgeous light blue all summer. There is a gas station here that has the plain non-named local genotype of Big Bluestem planted in mass. All of them look dried up, deadish and terrible in this drought summer we had here but its been extremely dry since spring. The best muhly grass for areas getting lots of shade time but at least 3 hours of morning or afternoon sun is Pine Muhly and the much bigger Deer Muhly (if you have a really big space). They seem to be impervious to drought no matter how dry it is, I read they thrive on drought and maybe thats true. Pink Flamingo Muhly grass down on the dry hell strip is a giant. Don't fall for that "fits in a narrow space" malarky. Its the biggest grass I have.

There are grasses that you can severely whack and there are others that can only take combing thru with a rake. That is a new question that has come to light as gardeners are observing that some grasses take well to pruning and some do not. Personally, I once severely pruned my muhly and it did not like it at all! Since then, I only take thru it and it responds very well to that treatment.