The chip that I removed the heatsink from, on the SP20, would not reach > 0.60V until I applied epoxy glue to the glue spots and pressed it until it stuck w/o wobble.
The 2 screws do a crappy job of applying uniform pressure on the die. Air is a great thermal insulator.
Ever seen a heatsink bolted on to a large die GPU with just 2 diagonal screws?
Once the 2 screws are completely tightened you're saying there isn't enough pressure on the die? Would it be possible to add a washer to each screw between it and the top of the heatsink to increase pressure?
There are spacers on the two screws which limit the amount of tigtening force to protect the die. 2 screw setup is not the most stable, since it allows for wobble.