I've had teeny trout like the one you have there Jim from Ennerdale when moving position obviously wading in a little bit with a fly near my feet lifting up to cast and finding a little bandie on there.
That's massive fluf.
I've managed huge browns to 5cm and the same with grayling. Okay when using light gear, but with heavier stuff, you think you've got weed or leaves. Though they do pull back on you more.
The smallest of both species I've had have been about the 4 to 4.5cm. Sure put a bend in 3lb tippet.
This is mine caught on the Tweed at Melrose. I honestly didn't know it was on there, initially thought it was a leaf or debris. I don't have particularly large hands either, so I would guess it is around 2 inches long at most.