Heat transfer equation set solving strategy

Hello,

in an example I posted in another thread, I was showing a model for a heat transfer problem including non linear terms, namely radiation. Some of those therms are rather small because of multipliers.

When vaying one specific temperature in those terms the solutions are varying wildly depending on the solving algorithm defined when right clicking the solve statement.

But there is another question I have:

Now I have one side of an equation multiple times in the set of equation, because I cannot find another way to assign three equations to each other.

Could that be part of the solver problem?

My next strategy would be to try out without the small radiation terms having T^4.

many thanks in advance

best regards