Yeah, it would be reading less than the maximum so the fuel tables are still maxed out and not defueled.
It does sound like you read the sensor that started it at the atmospheric pressure, 14.7 at sea level? So I would be inclined to think you really only have a max of 18PSI of boost, which sounds right for a stock 7.3 Superduty.
If you look through, there's another sensor to pick that'll start you at 0 PSI.