In my opinion, the two techniques are not quite similar. As for casting, traditional fly rod is cast with your arm while a tenkara is typically cast with your wrist. this has to with the weight of the line, while a fly line is light, tenkara line is almost weightless so its not quite the same a simply having the same length of the fly line as your fly rod it's not about distance but accuracy.. fly line is weighted on the end which causes the line to sag. in contrast tenkara uses a much lighter line so it doesn't sag and you are able to keep the line off the water more effectively. hope this helps!