Dwight Sounder said something to the effect that area of a block doesn't
matter, you can put it on end, edge, or whatever and the greater pressure
will squish it until you get the same area of contact. I erased the orig
post so can't quote it accurately. I think it was a quote from a book?
At any rate I think to blocks of wood on a table, such as a typical intro
physics lab this is not the correct mechanism. I believe that we are
looking at interlocking asperities and that a greater normal force makes it
harder to get the little buggers up and over each other.