DTP,
To answer the second half of your query, have a look at this thread here:
Hovering Downwind
Essentially, it doesn't actually require more power to hover downwind. It's just that slightly poor handling on the part of the pilot can tend to consume more power.
I'll let the assorted aerodynamics experts answer your first query.
HTH,
B73
Oh, even if your textbooks don't have the answer, the subject might well have been discussed on here already. Remember, the search function is your friend!
