Screening can be called anywhere on the court.
Also, it doesn't matter what your intent is, if you illegally set a screen and contact the defender, it's a foul.
My favorite
call has always been calling a foul on a player who sets to "box out," but then extends his hip and pushes his opponent a good five feet. They always protest when the whistle blows and I just respond "when you push the guy that far, it's not boxing out."