Right.
TMA will require you to REFINE your solution as you track the contact.
Again, its not radar. It takes time and some guess work on your (and your auto crew's) part.
You're tracking the relative motion of BOTH platforms, which is why your speed is a bit low. As it is now, you're both effectively standing still.
That can throw a lot of error into the TMA data you're working with.
Instead, look at what you already KNOW about your contact:
-He's moving slowly. Three knots is a very comfortable pace if you're walking, nevermind driving a sub.
In the big picture, he's not moving at all and can thought of as a point source.
If your goal is only tracking, you already know enough.
If your goal is to take a shot, remember that your fish move fast and their seeker cone is pretty wide. Your task is to have your fish go active when the contact is a little ahead of the seeker cone, say 3-5 thousand yards or so.