This is because the radiator is
oriented opposite to the gravitational force only. If one wants to
account for ALL forces involved then one must include with gravity the

Gravity has no measurable effect on electromagnetic radiation.

Thus to be in equilibrium a radiator
must be tipped to include the Coreolis force

The coriolis force does not effect electromagnetic radiation.

which then allows for a
spherical radiation pattern ala Poynting's vector where the forces
within the boundary equals ( and opposite) that outside the boundary
and is in a state of equilibrium

How is the Poynting vector related to boundary conditions. What
boundary are you talking about?