I find these ones hard to ID. The labellum seems to protrude quite a lot, and the flower is not very dainty, so it seems to fit aestivum over decurvum. It also looks a little more reddish brown than usual. Did you see any others on your walk?
I saw two others in different locations, both looked the same with a long tongue and reddish at the top but otherwise green. I also thought it might've been a green form of coccinum, but hard to tell.
That's what I was trying to work out. The lateral sepals seem to be a lot longer on this plant than the coccinum other people have reported. D. aestivum and decurvum typically have quite long lateral sepals too, so I think your ID is correct.
Hi Matt thanks for revisiting this flower, I always had it on my mind for some reason, might have to go back in a few months' time to have another look at them again.