It takes some very careful searching on the lower slopes.
7 years of checking this colony and I can certainly vouch for this! You really need to put the time in.
I might be inclined to phone the warden (his number can be found online) in advance to actually confirm flowering plants are present. The site is pretty remote too.
As already mentioned - lots of Heath Fragrants there, even more Heath Spotted and a handful of Greater Butterfly.