Do a search there is a thread a week on this literally. Most people will tell you use the tripmeter. They seem to be better first half of tank. There usually not off by 1/2. You saying at half tank reads empty?
There is away to adjust, I never bothered. Mines not under warranty anyways.
I manly use it to tell me its full. Sometimes forget to reset, and next day try remember. Suppose I could also look in the tank. There is an arm that cane be bent/adjusted. Since its new might want to.
Like I said most people claim best for 1/2 of tank.