I preface my comments with admitting I’m not an expert at this at all.
As others have mentioned I get good turnover with a level line the length of the rod or a bit longer and don’t need longer lines in most waters I fish. And I find line and fish management with longer Tenkara lines are more difficult than using a fly rod and reel, which are the better tools for me in those situations. My reasons for using a tapered Tenkara line are increased visibility while maintaining (or increasing) stealth, and reducing the amount of expendable fluoro tippet that is rather costly and unfriendly to the environment if I snag up and lose it.
I take level #3 to #4 fluoro lines and bloodknot an 18" tricolor section of Orvis 0X .279mm Chartreuse, orange, and white nylon sighter that brings my line length to about the length of the rod. Then I bloodknot about a 12" section of 6lb .229mm fluoro and terminate with a tippet ring. Finally I use a 3’ section of (usually 5X - ~5lb) fluoro tippet.