Does the arm move in and out freely at the hinge? It should be easy to pull the wiper arm out away from the vehicle. My original wiper arm had a tight hinge that was causing the wiper blade to miss a lot of the glass (I didn't realize that the hinge was tight and causing the problems at the time). I tried bending the arm itself, but that gave me mixed results. I ended up replacing the wiper arm with a brand new OEM Ford part, and this is when I noticed how tight the hinge was on my old wiper arm. Since I installed my new wiper arm, the blade now makes great contact with the glass making for a perfect streak-free swipe.
Try lubricating the hinge with some lithium grease. My original was so tight that it would stay out if I pulled it away from the vehicle. The new one that I installed will not stay out like that. If you want a new arm, you can get them on eBay for around $40 if you get a new OEM Ford part.