Derek,
Thanks for these references. Unfortunately, I only have access to two publications.
In page 26, Aart de Wachter does not mention (for what I saw) the 30 m² kite with a mass of 8 kg, but Flysurfer Pulse2 6.0, 6 m², with a mass of 1.6 kg, for a normal wind range of 6.5 – 21 m/s.
“Analysis of the maximum efficiency of kite-power systems” (S. Costello), table 1, mentions SkySails’ kite of 400 m² with a mass of 320 kg.
400/6 = 66.66…
320/1.6 = 200.
The exponent is 1.262 (or 2.524 if the size is the basis).
Maybe not as far as we initially thought, regarding the flexible wings.