After looking at some of the 1998 D Close AM error pics online, it looks like they all have the A and M characters touching. The Wide AM variant has a noticeable gap. However, my example (first pic) looks to be somewhere in between the Close and Wide AM variants. Is mine a Close AM, Wide AM, or a new "mid" AM? The FG matches the Close AM. Thanks in advance!
It is a Close AM... no such thing as a Mid AM 1998 S Mint Close AM is the rare one to look for. Your 1998 D is normal.
If the die is polished the field is ground down and due to the sloping sides of the letters the space between them increases. That is why some Close AM's are touching and others have a small gap between the letters.