I had the good fortune to take one of Simon's Workshop Classes.
I was having problems with a furled leader and a 14' rod and the GS 7/8. Simon had me take off the furled leader. Simon then tied a Rio
15' Steelhead Leader on the line. Then, we put a loop in the fishing end of the leader to loop the tippet on. The whole leader and tipper was about 17' long.
The difference was so positive and dramatic, I have never used anything but the Rio
15' Steelhead Leaders for dries, intemediate flies and skaters with all of my two handed rods. With my Sage 5120, I have a little problem getting the fishing end of the floating tip and the leader loop in past the rod tip. The rod is shorter and the eye at the end is small than my other rods.
If I use a furled leader for deeper water, I try to make it and the tippet about 15' long.
With sinking tips, I use the shortest tippet I can get by with. Years ago, I called Jim Teeny to ask him about the length of leader to use with his T series lines. The local fly shop had recommend 9' leaders. In clear water a standard non weighted steelhead fly sometimes could be seen floating up 5' to 9' above the tip the T line.
Fortunately, Lefty Krehl was visiting Jim and got on the speaker phone. Lefty advised me to use as short of a piece of tippet as I could get by with from 12" to 18" with any sinking tip. In clearer water 18" to 36". That was probably some of the shortest and best advise I have gotten in my recent fly fishing journey re fishing deep.
Lefty's advise works in our rivers for shad, trout, steelhead and salmon and also in the local Delta when fishing for Stripers with sinking tips or T14.