Come on, those gauges are the best that $1.95 can buy!
Yes, if you have a good dealership service department they could "tweak" the sending unit float rod in the tank to make it read more accurately at the bottom end of the range. Unfortunately, most won't do anything but tell you "they all do that" or "that's normal", or they might try to replace either the gauge or the sending unit if they think H-D will honor the claim and pay them for it. That might not make any difference, however, since this seems to be a widespread problem related to how H-D had the new sending units designed. Be thankful, I guess, that you don't have the gauge from the days of the 5 gallon tank, when we ran out of gas while it still showed 1/4 full.
Jerry