Consider 'r' as the handle length and 's' the resulting arc, or movement produced as a result of a given handle movement. As you can see in this image, with the same amount of movement (or angle you change the position of 'r', your handle), with a short handle, or short 'r1', the movement produced is the small arc 's1'. But, with the longer handle, or 'r2', you end up with a longer arc 's2'.
Since the kite experiences the inputs from the ends of the handle, it is experiencing the resulting 's' of a handle movement. Longer handles results in a greater input to the kite from a given movement of the handle. It essentially exaggerates any motion you make. Conversely, shorter handles result in less input to the kite.