You already have line of sight but you can't get High-def? I've never heard that before...
To pick up the HD channels you need a new dish and have to change the aiming point slightly to pick up the new bird. Maybe the new angle brings some more trees in to play.
Yep, I have a very narrow break in the trees that enables me to get the SD birds, but the HD birds are behind 5 or 6 really big ones that I'd be loathe to cut down (would seriously degrade the beauty of the yard as well as cost a ton).
