Believe it or not, I don't think JS knew the BofM very well. I read somewhere that he never quoted from it when giving his many speeches. He was not the book's author and I think it took some years after the translation for him to realize it took place in a relatively small area.
That's a quotation from a Facebook post by Doug Christensen, the President of the "Book of Mormon Archaeological Forum," a group of Mesoamerican theorists. He posted it in a closed FB group so you have to be a member to read their posts. I don't know of Mr. Christensen has announced his position publicly, but it is implicit in all of his comments on the topic, as well as the comments by others who write for the BOMAF.
Throughout my discussions with Mesoamerican advocates, I've found them to be highly defensive about their critiques of Joseph Smith's writings and sayings, as well as his mother's biography and the journals of his close associates and contemporaries. They dismiss every reference (including in the D&C) that supports a North American setting for the Book of Mormon, instead favoring three short articles in the Times and Seasons that lack a byline or signature. They resort to incomplete wordprint analysis to assert that Joseph Smith wrote these three articles. I'll address each of these points in separate posts, but for now, anyone following the debate must be aware that the Mesoamerican theory will lead you directly to the same destination that Mr. Christensen has reached; i.e., you will have to conclude that Joseph Smith did not know the Book of Mormon very well.
Realize, too, that BOMAF has several emeritus General Authorities on their Advisory Board:
So far as I know, they have not publicly agreed with Mr. Christensen's belief that Joseph didn't know the Book of Mormon very well, but by virtue of their association with BOMAF, one can only infer they do agree.
Here is the post in context (at the bottom of this excerpt). I've deleted the name of all the participants other than Mr. Christensen.