Fly speed is much more important than fly depth. Slow it coming across for the big grab! Every Winter steelhead on the Sandy, in my boat, this year has been landed with an unweighted fly and a lighter weight sink tip.
Don't just mend and let slack create a belly in semi-fast, greasy water. Instead mend and keep tension to create an almost "hangdown" effect through the whole swing. After the cast lands down, mend it all the way to the fly. Get rid of the hook at the end. This is done best with a high stab of a mend while keeping your rod tip out and high over greasy seams. Slowly and smoothly let the fly lead the rod until the swing is about half done and then transition the rod downstream until the rod leads the fly through the last half of the swing.
In soft or even flows it is good to allow the rod to lead the fly across the current. In this type of water you can let the fly line belly some and allow the flow to swing the fly in a natural manner. They grab hard with this presentation.
Its all about presentation and all too often I see anglers make the same exact mend on every cast and in every run even though the structure, current, and flow speed are different. Pay attention to what the water is doing and mend accordingly.
