Why is ther no formula to figure out port volume?

There's several. I have one too, but it's rpm specific, and all programs are simple math engines that use various assumptions. Nothing can simulate or predict everything. The parts and system are mechanical and math predictable. But that does not take into account the fuel dispersal or the flow dynamics and burn characteristics of an individual cylinder. We know how much air goes in. But things like the temperature change of the air as the fuel disperses into it, the amount of air displaced by the fuel in the induction system, the amount of liquid fuel that enters the chamber, the qualitites of that fuel, the airflow (quench) that the chamber feels, and the wave tuning of a particular intake system all add variables that cannot be 100% planned for cylinder to cylinder. Accuracy is never 100%, and the simplest way to limit the issues that lead to "averages" and larger possibility of error, is to limit the power range that you are looking for. Which is why the one I got does a single rpm point.