I believe that the smaller the diameter, the faster a weighted fly will sink. When fishing BH midge pupa/larva patterns under an indicator, I want that fly down in the zone Quick! I mostly fish such midges on 6X, but in gin clear tailwaters in winter, it seems 7X to have a slight advantage on 22 and smaller sz midge patterns. That is why I spring for the pricier Seagar or Froghair flouro tippet on 6 and 7x.

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