Is it the required size of the wings for radiative cooling then?

Just picture a square based pyramid, like a pyramid from egypt, thats the rough shape. Lets pretend the bottom is square. For thermodynamic analysis, we can just pretend the scale is irrelevant, it could be 4 cm x 4 cm base or 4 km x 4 km base. Now stretch the pyramid so the height of the tip is 3 times the length of the sides of the square base, so 12 cm or 12 km in the random examples above.

If the base were a solar panel aimed perpendicular to sun, then the tip is facing away and all side triangles faces of the pyramid are in the shade.

I voluntarily give up heat dissipation area on 2 of the 4 triangular sides (just to make calculations easier, if we make them thermally reflective -emissivity 0-, we can't shed heat, but also don't absorb heat coming from lukewarm Earth).

The remaining 2 triangular sides will be large enough that the temperature of the triangular panels is kept below 300 K.

The panels also serve as the cold heat baths, i.e. the thermal sinks for the compute on board.

Not sure what you mean with wings, I intentionally chose a convex shape like a pyramid so that no part of the surface of the pyramid can see another part of the surface, so no self-obstruction for shedding heat etc...

If this doesn't answer your question, feel free to ask a new question so I understand what your actual question is.

The electrical power available for compute will be approximately 20% (efficiency of solar panels) times the area of the square base L ^ 2 times 1360 W / m ^ 2 .

The electrical power thus scales quadratically with the chosen side length, and thus linearly with the area of the square base.