yeah that's what they say. There is really no standardized formula for that kind of fishing.
Traditionally you want to match the stiffness of the butt section to the end of the fly line...so 25lb for 6 weight and up 20lb below that otherwise the leader will hinge. Casting those long leaders isn't all that precise or demanding in terms of presentation. You are not casting far or caring much where it lands - get it out a ways and let it sink.
As I said I mostly use a commercial tapered leader for floating lines. For sinking lines for most cases I use 3 to 7 feet, shorter for fast sinking lines. For 3 or 4ft just use tippet of maybe a foot or 2 of heavier line (12 or 15lb). For a clear slow sink I'd use the Pallot formula and taper it to 6 or 7 feet. Some folks go longer.