Indeed 10x (the distance between the two tethers on the ground rotor) is what we see on your initial post and also likely on achievements.
Some suggestion: I think you need a tensioner device for the tethers. This device could be (two) winches settled on the ground rotor (generator) and allow to vary the tether length between the two rotors in order to stretch them. At the same time the tensioner device can allow measurements according to the variations of the axial force (more or less that generated by the lifter kite).
In my opinion in the kite field autogyro-like rotors have a higher tangential speed (tip speed ratio TSR) than other kites and would facilitate a first realization of a physical flying (with a lifter kite or a slew plate for cyclic pitch control) model: two tethers, two blades. That said the use of two controlled separate kites could facilitate scaling.