That may be however , after using the tractor beam to bring the Tantive IV into the docking bay the Stormtroopers used a gangway to directly connect to the boarding hatch which they blew out or in. I am not saying that TIE Boarding craft did not exist, I am mearly pointing out that they did not use them in the movie. When Threepio looks back at the Tantive IV from the escape pod you clearly see that there is no space between the docking bay and the captive ship for a TIE sized ship to operate. -Grand Moff Conway