I was probably wrong about the extension. It is likely that the difference in the the length of possible extensions with the different kite sizes is already calculated in the front bridal of a high V kite. This is due to the increased angle of the V with the sizes. But overall the front lines of the low V (e.g. North) bar may need only about a 2cm uniform extension that I calculated for a 5m kite, but I think it should be the same for larger sizes. That 2cm may not make a lot of difference, so it is important only if someone wants the absolute max power out of the kite..., but that may risk back stalling... (bitter-sweet memories from the time of no-depower 4-liners

)
Cheers