Excuse my confusion, but isn't h in convection a macro-geometry dependent component? There is characteristic length in the equation of Grashof Number that we use to calculate Nusselt Number, which again is used to calculate the convective heat transfer coefficient. Again, characteristic length is dependent on the shape and orientation of the geometry, so doesn't it make h a macro geometry dependent component?

I understand how the area in the convection equation accounts for the geometry, but apart that, the h value in the convection equation also relies on the geometry of the part. And this dependancy of h on L (characteristic length) is not linear either. This is where the complexity arises if I want to change the geometry, as in, should I consider the change in geometry, thus change in characteristic length in the value of h? My understanding tells me not to. Please share your thoughts on it.

I have added pictures of the actual model.