I prefer to make my own leader so I can use my prefered make of fluorocarbon line.
nail/needle knot (3 or 4ft) 10lb mono to 7/8 weight fly line, then 8lbs fluorocarbon with 4 turns water knot (3 to 4ft) leaving dropper on fluorocarbon. then 6lb fluorocarbon again with 4 turns water knot.
For stocked lake/reservoir
If all else fails & I really need to catch a fish for tea, then I use a lure direct to the 8lb fluorocarbon
When fishing with a 5/6 weight fly line then I'd use 8lb mono first then 6lb fluorocarbon then the 4lb fluorocarbon.....2 lengths of 4lb for extra fly,
I find that having the flies closer then about 3 to 3 1/2ft spooks the fish.
other will have different ideas which work for them, you will have to try a few ways so you can find what works best for you

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Paul