We are having the exact same issue on a new to us 4350 FC. We are now building in a 10% error factor and it seems to be more consistent. I thought we should start over and do a distance calibration again. We have also found we have to work quite hard to squeeze 400 bushels of inoculated peas into a 430 bu tank. We never know densities and with the old 2320, we always used the average density and was usually pretty close. Never liked calibrating and guessing at tank levels. Always nerve wracking whether you will have enough to finish the field. We grow a lot of different crops so go through that every second day or so. Good luck!