This topic is like a counterpoint to the interesting topic Scaling in numbers rather than size.
The main argument I can make is the tether as an irreducible part of an AWES. If we intend to harness high altitude wind energy, the tether length will be the same whatever the dimensions of the flying body. So small flying bodies would lead to a forest of long tethers with high mess risk.
As a resulting assumption the flying body should scale with the tether length to maximize the space. A tether is a little like a tower of a ground-based wind turbine. The tallest towers are about 120 m, leading to larger rotors of 150 m diameter. The proportions should be the same for AWES: the tether length should be equivalent to the dimensions of the flying body or its maximized swept area.
As a temporary conclusion the suitable proportions would be a flying body of 1 km for (a) tether(s) of 1 km.