Chad, as a brand new subscriber, I just wanted to share that I totally found this icon/its meaning to be non-obvious. This was after (a) expecting a Paste FEN option to be available, (b) looking for such a Paste FEN capability, © noticing that indeed there was a FEN field under the board.
The usability problem for me likely resulted from that “edit” icon being a little too small. From my viewing point, without getting too close to my pair of 27" displays, it looked more like a “share” icon.
The only way I now know is that I searched the forums for “FEN,” but someone like me that expected it and looked for it, I shouldn’t have had to search the forums for it.
Perhaps making that icon just a little big larger would help this function be more discoverable.