Magnum heads on LA block H.p increase

Sorry I'm not trying to offend anyone. I like all mopars.
I'm just trying to figure out where people are getting thier numbers for calculating volumetric efficiency? And longevity? I'm not saying magnum heads are all that but out of the box stock with smaller valve they flow with the X and J heads with larger valves out of the box stock. So yeah depends on complete build like pistons compression, deck height ect... correct?