Yes, I want to input HTC and Free-stream Temperature(which isn't all that free in my case)

the following image describes my problem, this is the longitudinal section of a finned cylinder(cylider=1, fins=2), with a melting/solidifying substance(=3). 2 and 3 forms a convective boundary with 4(which is air, which in turn is in contact with another metal 5, which gets heated/cooled according to the heat give/taken by cylinder 1). The thing is I want 1, 2, and 3 to be COUPLED amongst each other, Meanwhile, in between (2,3) and 4 is to be a boundary condition with CONVECTION mode. 4 and 5 are to be coupled. The thing is that Ansys is treating the boundary between (2,3) and 4 as a kind of interior, even though I can turn it to a Wall, only coupled, temperature and heat flux modes appear for thermal boundary conditions. It just doesn't fit in with the system Ansys is using in the background. Is there a way to get around this issue. Only the outermost boundaries, of the surfaces, can be specified with convection kind of B.C.s, I get that. And I have figured that eliminating Domain 5, and 4 altogether, makes the boundary (2,3)-4, an eligible boundary for convection, and then inserting a UDF for free-stream Temperature could work as a substitution for the heat source/sink, that 5 is. But, I don't want to do that, please tell what am I naive about here?