Why is Pro Stock Dodge down on horsepower ?

Or could it be the Gen 3 hemi isn't really a hemi like the Gen 2's. When the 2's came out they blew everything away. Although with head development they, the pro stockers, could produce maybe a better combustion chamber than Mopar came up with. Of course I don't think anyone would let us take a look and let us compare it to a stock head.