The formula is only as good as the inputs. The displacement, rpm, and conversion factor (3456) are all hard numbers. The VE is not. Depending on engine speed, cam profile, head capability, etc. the VE can be all over the map. As such the formula is only good for a guideline or an initial guess, nothing more.

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".