I agree. Wire size needs to be stepped up for the long run. I went 1/0 from the battery switch back to the transom (overkill) terminating at a power post and smaller 4GA thru the transom to the motor. My rigging tube is different from stock, larger diameter, straight run and lots of room.
If your boat is stock you may run into issues getting the wire pulled thru.
My run was about 12' to the transom and another 6' from there to the motor. 2ga would have probably been sufficient for my entire run. Check out the 3% voltage drop table as published by West Marine.
http://www.westmarine.com/webapp/wcs...arine-Wire.htm