Keep in mind that heat transfer in most BEM software is 1-dimentional, i.e. a balcony fin will only transfer heat in the direction of its surface normal (vertically in this case).

@dradair's suggestion of Therm is a good one. It could be used to calculate the assembly's U-factor, which could be used in a whole-building model.

An easier option is to use the values from the Building Envelope Thermal Bridging Guide (Morrison Hershfield, 2019) to derate the thermal performance of the assembly in your whole-building model.