Hello Imogen. Welcome to the forum.
Because I have mixed plantings, I hand water my tiny garden once a fortnight in summer.
The miscanthus never flags in between waterings, no matter how hot it is.
I also have Stipa tenuissima and Deschampsia cespitosa. They are equally as happy on my regime. The stipa seeds around a bit, but not enough to be a nuisance.
I don't know how they would do with less watering, perhaps someone else who doesn't water during the summer can tell you.
I have just planted a new Stipa gigantea and a Muhlenbergia capillaris.
This will be their first summer. I am looking forward to seeing them grow.
I can tell you which other perennials are happy in my garden, but I had better do that on a separate thread.
Daisy