DeltaFree,
The whole pressure increase buisiness is interesting, it "seems" right, and it is not correct. This "mystery" was studied about 3/4 of a century ago, here is one reference that discusses the ability of ground proximity to reduce induced power. Note that in 1928 there seemed to be no need to use the word "pressure" in the NACA study that measured and explained ground effect:
http://naca.larc.nasa.gov/reports/1928/naca-report-265/