That little copper plug sticks up half a millimeter so that's the only area contacting what you're trying to cool. Has anyone leveled that off?
I would think ideally it would be pressed further in so no material is lost.
I don't know how thermal expansion works. Would it theoretically be easier to press them together more if both pieces were cold, or if the aluminum were hot and the copper cold?
Could just stick it in a vice and see what happens. Just thought I'd ask.