This makes a big difference because the river Sidon flowed past the city of Zarahemla. Most people agree the head of Sidon was south of Zarahemla. If the head was the source, then the river flowed north. If the head was the mouth, then the river flowed south.
The entire M2C theory depends on this term meaning "source." If the River Sidon flows south, there is no scenario that fits Mesoamerica.
Below, I'll show that the most likely meaning of "head of Sidon" is the modern concept of "mouth" of the river. Of course, this fits the upper Mississippi River. The M2C scholars insist there was a river flowing north from Nephi to Zarahemla, although the text never says this is the same river as Sidon. That's because the Tennessee River does flow north from Nephi to Zarahemla, but it is separate from the Sidon (Mississippi) River.
IMPORTANT: Translations of the Book of Mormon have changed the text to promote M2C.
Instead of translating the text literally, the translations use the foreign language equivalent of "source." This is an obvious error. The translator's edition, which gives interpretive guidance to translators, reflects this meaning.
Consequently, translations of the Book of Mormon are misleading readers throughout the world.
The current translations are falsely imprinting M2C on members of the Church who don't read English.
I discussed this over a year ago here: http://bookofmormonwars.blogspot.com/2017/05/more-on-sidon-flowing-north-and.html
At the very least, the translations should remain faithful to Joseph Smith's translation. In English, the term "head of Sidon" is at least ambiguous. I can remain just as ambiguous in foreign languages.
There is no justification for changing the meaning of the text to conform to the M2C scholars' interpretation.
To make matters worse, it is much more likely that "head of Sidon" does not mean "source."
Theodore Brandley argues that "head of Sidon" means the mouth. I agree with him (as I've written about before). Brandley wrote a nice article on this here:
Here's an excerpt, followed by examples that support his approach. The examples are worth reading if you still question the meaning of the term.