The crank sprocket has edges on it which will position the belt in the proper position. Looking at that first pic, my 420a TB sits about the same position. It's closer to the edge, with more space on the back. Here's a pic
(Excuse the mess... very dirty shot)
If the sprocket is not in all the way, then of course the belt will position properly to adjust. However, it's near mpossible for the sprocket to NOT be in the right position. That would be bad. Is the tension good on the belt?