By him stating that a extreme FOC light arrow outpenetrates a reg FOC by 50% doesn't that negates the heavier arrow will penetrate more because of momentum.
You may want to read this page:
http://www.tradgang.com/ashby/2005update6.pdf
and this one, which is very good:
http://www.tradgang.com/ashby/2004update2.pdf
and another very good one for his overall explanations:
http://www.tradgang.com/ashby/2005update5.pdf
He has many different studies going on, and it actually takes a long time to read them all and understand them. I have. When done, I really don't see how anyone can disagree to any great extent with his methods or conclusions. They are far and away more in-depth and thorough than anything else out there.
When done reading this, you will see that he finds absolutely no correlation between penetration and KE. He also finds that momentum is only a starting point. He demonstrates clearly that heavy weights are king for penetration and that arrrows that derive their momentum from mass vs. speed are clearly better penetrators, even if momentum is the same. He also points out that even though extreme FOC is very important to penetration, that only heavy weight will give "bone breaking" impacts. Speed will not do it, extreme FOC will not do it. He even demostrates that a 700 grain arrow shot out of a 55 lb bow is almost as effective at breaking bone, as the same arrow shot out of a 70 lb bow. He concludes, the overiding factor is weight over 650 grains. He also states that extreme FOC arrow appear to lower this bone-breaking threshold only slightly.