Cyclic Rick,
the vectors of the low pressure area on top of the disc and the high pressure area below the disc both point upward. They don't cancel each other but make your total lift vector together.
Cran,
nice of you take precious time to answer questions on this very very very simple peoples forum. (Just kidding because of the opening in your post!)
I figure all you wrote pertains to a stabilized hover in a theoretical no wind situation with a constant AOA?? Now there is no hover without extensive vortices production. How can the mentioned downwash formula work without taking in account that the outbord section of the disc is busy with the production of vortices rather then lift?? Should the area covered with vortecies production simply be subtracted from the total disc area?
sp