My apologies for not recognizing you as a new member. Welcome!
Typically, a Tenkara line is one to one and one half the length of the pole. Some folks choose to push the envelope. If you saw video of people using longer lines they were not being consistent with the spirit of Tenkara. Of course, there are those who claim true fly fishing must be dry flies. I think you are required to wear a twead jacket with leather patches on the elbows too.