5 square inches? The problem is that there are capacitors in the way of the chip, so you can't mount a big one.
Here is photo:
See the four orange capacitors that's in the way of mounting a sufficiently large heat sink? Anyway around this?
Solid copper spacers to raise ASIC level above other components.
However the small SMT components may then overheat due to lack of airflow.
Immersion is the only cureall for this design of boards top level.
Holddowns for the small sinks as suggested world take a board revision to accomplish.
I think since that chip is isolated (other chips show no signs of overheating), was a short from dislocated backplane or other damage occurred during ship.