Dave,
Nice wild guess, but the pressure is the same in or out of ground effect. There is no "restriction" and no pressure rise. The flow is bent by the ground, which reduces the outflow, and makes the rotor behave as if it were larger. The efficiency rise of the rotor means it can make the lift needed with less power.
The issue that all the pressure fans miss is that there is more power efficiency, not more lift. This efficiency is brought about becuse the ground changes the direction of the flow, NOT its pressure.
However, since we have gone through 138 posts to circle back to this, and the last several posts all simply repeat the pressure assertions of the initial posts, we are truly stuck. If you cannot see that the answer to the ground effect efficiency improvement is not a pressure rise, it is simply a shame. Quel damage, as they say in Paris.
Have a Merry Christmas, guys!