OK, Gregor, thanks for clarifying.
With that lining setup, I could go as short as 9ft for SA and up to 2X rod length for very high-energy scandi style with a compressed stroke.
The trick for fishing shorter leaders with scandi heads is to make sure a couplethree feet of line form part of the anchor. This requires either excellent, excellent anchor placement or SA technique. Some prefer a heavier head for that to make timing easier, but I usually don't. Very handy for tight quarters and brushy banks.
For a light, fast, energized scandi cast style, the longer leader is an advantage because it's easier to obtain a consistent anchor while still having all of the head in the D-loop. This can lead to addictively high line speeds.
That was an insightful and thoughtful question, I hope this answer provides you with some insight. There are widely varying opinions on this stuff:roll: but that's mine.