I know it has been discussed many times on here about the issues with the fuel tanks and gauges on these boats. I finally got tired of my gauge not reading correctly so I pull the seats out and pulled the gas tank out. I removed the sending unit and found it is a 12". Based on some quick calcs it seems about right that my gauge reads E and I have about 1/2 tank still left since the bottom 4" of the tank contain about 29 gallons of the 51. So my questions is, I am replacing the sending unit with a longer one so it will read the lower part of the tank better. They say the sending unit should be 1" shorter than the tank, why is that? Can I install a 13 1/2" unit, that would mean I am only 1/2" off the bottom