It sounds like you are creating too long of a head for the line. Adding a 15' (?) section after the head of the WF isn't how the line was intended to be used.
Depending how deep you want to go, I would look into the streamer tip lines, ie WF6S6 which is a single line with a 15' sinking section designed into the head. If you are looking for a bit more versatility, look at the versitip kits. They have a hinge design, but you can change out the tips to get floating, intermediate, type 3 and type 6 tips. 8wt and up also include a type 8 tip I believe.