Place some Radio Shack Anti-static Foam cut to length of the heat sink and about 1/2 ” tall and place under the retention clip. When you secure the sink to the CPU socket the foam creates greater pressure, pushing down on the CPU so the sink sits more level! Worked great for me!
Just squish the foam under the clip and it will make the sink sit much more level! Oh – you might want to line it up with the sink so it doesn’t stick out like the picture.