Here's what I have gathered information

The right line length to use is dependent on the kite size and the condition.   Given the same kite size, use longer lines for less wind and shorter lines for more wind. 

The standard line length is 23 - 25m.  In high wind, you may want to use shorter line length for more control of the kite; however, don't go shorter than 15m as you will loose much of the "jumpability" of the kite.

Hope that will do