Key thing to remember - increased contact does not increase pressure, but generally increased pressure will increase contact. Pressure is the more dominant of the two.
Let's flip the problem, In engineering a common device used to limit heat flow to sensitive components in an assembly is a “Heat Dam” shown here in figure #3 Where the heat flow is “thermally choked” by reducing the contact area to material limitations. Restricted heat flows with misaligned contact, too little contact, too little pressure, too little compound anything that can restrict flow creates a heat dam.
Heat flows on a differential from hot to cold but if you are thermally choked at a point in the thermal cascade downstream improvements in thermal conductivity offers little difference in performance and shows up as reduced deltas of only a degree or so between compounds or what I sometimes refer to as homogenized test results.
Now back to your situation, your analysis of having contact in the right area is correct rather than forcing the heat flow across the IHS to the sink which is a thermally choked condition pushing to the material limit of the copper. I believe the molehill change from mountain allows a thermal compound to work as designed now by being able to bridge the gap from IHS to sink as in Figure 1. These are the thresholds or tipping points for you guys and all your ducks need to lined up in detail to squeeze the most out of your systems.
For further improvement possibly a degree or two from improved contact and another 1-2 from increased pressure although I lean towards more pressure at this point.
If you could figure a shim to tighten down the sink some more...
