Putting all secondary effekts aside, scaling wingspan will scale the tether force by x^2. Scaling tether diameter by x scales the tether cross-section-area, and thus the strength if the tether by x^2 as well.

If you keep the tether length constant, you are effectively changing the design as tether drag will be relatively smaller than kite drag. And kite will fly faster. But this would be breaking the scaling law above.

But: you could always scale wingspan without scaling tether. At one point, the kite will not fit anymore, as the wingspan and turning radius geometry will limit what can practically be done. Therefor I believe it’s more correct to consider «universal» scaling like I started out, and then say that scaling tether length by a lesser factor should be considered a design change. Also note that the «universal» scaling laws retain effective glide number of kite and tether, which is why it is possible to even state the scaling laws in the first place.

Reynolds number effects i did not put in there, nor wind gradient effects. I believe these should be considered secondary effects. Less important for a «rule of thumb» approach. Probably quite important though for a detailed design.

Wrt fairings, i would consider this a design advantage, that would most likely scale by the said rules once implemented in small scale and then scaled up