Reddit mentions of Small-river fly fishing for trout and grayling

I'm not familiar with the Eden (one day hopefully), I fish Welsh border streams (Lugg, Clun) primarily. On these there are areas where I will catch primarily grayling and others trout, I'm not sure why. If anything I'm getting grayling in the deeper runs and pools and often in the middle of the stream. This book tends to support this theory that grayling will be more central whereas trout lie into the bank and around structure. Fly wise this should give you some ideas, bit of a shameless plug, but I use Gareth's flies and they certainly work ;)