Flux reports are providing you with how much total heat transfer rate is crossing the boundary. If this is positive, heat is entering the boundary and negative means it is leaving the boundary.
So, if you have a face zone (or a boundary) around your heat sink, the total heat transfer rate crossing this boundary might be the value you are looking for. However, based on your model, I would advise you to understand the energy balance in your system first. This will help you comprehend the numbers better.