Yes certainly in my experience on chalk streams in southern UK, small flies (<size 16) are usually the way to go for both trout and salmon. I’ve had grayling take dries in shallow water but a lot of the time the adage of “if you’re not hooking the bottom, you’re not hooligans fish” applies to grayling. In that regard, the peeping Caddis/jig hook flies are very effective seeing as the hook points upwards.
Had a couple of nice grayling to a black Gnat parachute dry the other day on a small free section in durrington just north of amesbury off the a303 thet were taking off the top in the riffleier sections
The fish can be really spooky. Fish as long a leader as you can - I fish 12'-15' and sometimes more. I agree with small flies - most of my nymphs are tied on TMC 2499SP-BLB #18 to maintain small size but a good gape.
i fish mainly small streams . My two favourite rods are the Vision Cult 9ft 3wt and Hanak Czech nymph 9ft 2t ( also has a 6 inch extension) . Generally smaller flies 18 and 16s Also look to the shallower water regularly catch in water a few inches deep .