There are a few other things to consider. The IC designs available for the Z (side mount) always have the inlet and outlet on the bottom. Several postings using modeling have suggested 80% of the air to be cooled passes through the lower 20% of the IC. The other is flow resistance (lag inducer). Front mounts with long paths offer more resistance to flow. Front mounts also affect the cooling efficiency of the a/c. Finally there is thickness. For SMICs, where larger area is not an option thichening the core helps but thin and large is the best.