You're talking about how they made an effects shot. I'm talking about what was mentioned in somebody's post, which if I recall right was about a STORY hinging on the size of the thing.
If the ship was a half-mile long at that speed it would have got chopped going through.
The script was written long before the effects were done. The door was likely noted in the script as being just big enough for the Enterprise
to fit through. Nevermind that the little tiny Jenolen
was powerful enough to extend her shields far enough to hold open the doors for a ship that was much bigger in comparison.