Can I specify a wall temperature = 200C on fins bases, The rest of the bottom wall will be completely adiabatic

I tried real wall and specify Tw= 200C but since this wall is not in contact with fluid, it does not allow me

I don't want to go to outer wall method where I have to specify outer fluid temp and heat transfer coeff.

To complete the picture, I am allowing heat conduction in solids (to simulate heat transfer through fins, I only specify material for the fins (the vertical walls)

But no material for the bottom plate, so any adiabatic wall condition (or isothermal condition) I am specifying I always specify on the inner wall of the bottom plate.

I have another case where fin bases and the rest of the bottom wall are both isothermal @ 200C. In that case, I have single surface (I did not split surface like I did in this current case). With one single surface, I can specify real wall at 200C and it worked OK.

Any suggestions to specify only fin bases @ 200C and rest of the wall adiabatic

Thanks,

Ayman