I know nothing about Bull trout fishing , but I like the colours of this fly you posted .
If you are looking to go with a smaller offering , scaling down the hook size also means to scale down materials , in my opinion .
My opinion here , not that it matters , but here goes .
Your tag is nice , it runs between the barb and the hook point . Personally , I like the tag to start at the hook point and move forward . I can't see a tail on this fly , so that's cool . You have dressed the butt very full (too much junk in the trunk) . I would scale that down a bit , limiting it to half or third the size shown . Good body work . I like thin bodies , they aid in sinking the fly . When using dubbing and you want that buggy look , use a thinly made dubbing loop . This will still give the bug look and will remain thin . That rib adds a lot of contrast , I like it . When dressing scaled down flies , I like to use thin ribbing materials and use wide spacing , it adds to the sparseness of the fly . It is important to use less materials in the wing as well . Get all the under fur out so it doesn't add bulk and stop the fly from sinking . Collars are difficult to master . The hackles look so nice when you wind them on . But it's this part of the fly that tricks the tyer the most and can easily over dress your fly even though you have done an excellent job scaling down . So saying that , I will make this statement , strip off one side of the feather and only use one or two turns at most . The collar hackle should not exceed half of the body length , one third is better . I sometimes go less if I wish the contrast to be muted .
Again , these are just my opinions and not meant to pick your work apart or to be malicious in any way
Mike