Heat transfer problem

Good afternoon, I have a question need some heat transfer experts help me to answer.

It is related to the heat convection coefficient.

For example, I have an object (blue)  as shown in the picture below that I have been defining its boundary conditions, including heat convection coefficient of 12.5.

And now I have it in contact with another object (orange). Can I still define the rest of the expose surface as 12.5?

If not, how do I calculate this difference or another value for it?

Do we have a way to characterize heat transfer coefficient for modeling?

Last one, is the value of heat transfer coefficient depending on the object? I mean object in orange, can I defind its as 12.5 on the boundary as well?

Thank you so much!

Jerome.