Bingowings said:
I read it (after ROTJ but the signs are there) that Vader is sensing Leia and mistaking her for Luke, knowing Han helped Luke escape the Death Star and shot up his ship adds to the assumption that the person strong in the Force in that ship is Luke (when he finds he isn't there he improvises the trap at Bespin knowing that Luke will feel the pain of his friends).

Dude, that's just Lucasizing.

Vader had no way to know where Luke was during the battle, so failing any hard evidence that he was fighting the walkers, the other logical place for him to be would be on the Falcon during the escape. And from a "capture the Rebels" perspective, he figured that's where Leia would be too, so it made sense to chase the Falcon instead of worrying about individual X-Wings.