Eric is exactly right here.

I'll take it a step further. One time I and another boat were on port going upwind. I was to leeward of the other boat which was overlapped to windward. I saw a starboard tack boat that I could barely take it's stearn just ahead. I could take the boats stearn perfectly leaving no room for my overlapped "freind" to windward.

He quickly asked for room because of the obstruction. I allowed it. Turned out bad for me because this allowed him to reach down on top of me when I allowed the room.

Lesson is that a starboard tack boat can also be an obstruction.