I don’t need some roundabout story as to why you use a 9’ leader. I run my 1’ leader and whack kings all year with skein. It’s not hard to catch a fish with skein and a short leader. The fact that you’re using this method with a fly tells me all I need to know. 😂Every year somebody hates my methods. This is not flossing.
All my fish I've caught with this technique is in the internal mouth.
With an approximate 3m length leader you're covering approximately 27m^3 of area (in theory) depending on river outflow conditions etc.
To make a point, I'll tell you a story from just last year.
There was a guy on the Big M using 1/4 ounce weights with a 3ft leader. He was not catching fish.
I explained to him his pencil weight was creating the most pull and most likely pulling his fly down the River. I told him to up his weight and leader...he asked me first.
Then I see him again, but now he has the right weight on, but his leader was still...3ft if that. Which means now the leader with the fly is under the fish.
The leader is now dragging the weight under the strike zone.
Big leaders doesn't mean flossing.